Palm oil is one of the most widely produced vegetable oils in the world and currently its production is being boosted with extending their use in making biodiesel (Lim and Teong, 2010). In 2012, Malaysia was recorded as the world’s second largest producer of palm oil with the production of 18.7 million tons on crude palm oil (CPO) (MPOB, 2012). However, the unsustainability of palm oil production has been constantly criticized because the large quantities of biomass residues almost 5 times the weight of oil production are a serious threat to the environment (Ahmed et al., 2003).
Generally, the palm oil milling process can be categorized into a dry and a wet (standard) process. The wet process of palm oil milling is the most common and typical way of extracting palm oil, especially in Malaysia (Salmiati et al., 2010). According to the industrial standard, the milling process produces wastewater in the range of 0.44 to 1.18 m³/tonne fresh fruit bunches (FFB) with the average figure of 0.87 m³/tonne FFB. It is estimated that for each tonne CPO that is produced, 5 to 7.5 tonnes of water are required, and more than 50% of this water ends up as palm oil mill effluent (POME) (Ahmed et al., 2003).
In particular, palm oil mill effluent (POME) causes a greater impact than the other by-product of palm oil production, of which estimated amount is 3 times more than that of crude palm oil (Wu et al.,2010; Yeoh et al., 2011). POME is a viscous brown liquid with fine suspended solid at pH ranging between 4 to 5 (Najapour et al., 2006). Moreover, POME is a liquid that containing high concentrations of organic acids with a COD level higher than 20,000 mg/l (Lam and Lee, 2011; Najafpour et al., 2006). POME sludge has malodour as a result of its high content in total nitrogen, total phosphorus and potassium. Most of the odorous substances derived from anaerobic decomposition of organic matter contain sulfur and nitrogen (Parivesh et al, 2008). As the population is increasing together with the urbanization in the nearby area around the plant palm oil mill, odour problem should be controlled to provide cleaner and fresh environment.
On the other hand anaerobic treatment is favorable for POME treatment as it can remove much more organics even with limited available nutrients. Therefore, anaerobic treatment processes have primarily been adopted for POME in the field (Poh and Chong, 2009).
Facultative ponds and open digesting tanks are the most commonly used anaerobic processes for the treatment of POME (Yacob et al., 2005). Although these conventional processes require relatively little energy to operate, they demand extensive land area and long retention time (Lam and Lee, 2001; Wu et al., 2010). Besides, a large quantity of greenhouse gases including methane and carbon dioxide is produced from open ponds and tanks these gases are emitted directly into the atmosphere.
Based on previous researches, it is proven that the effluent produced during palm oil production emits a highly unpleasant odour which will cause discomfort to the neighbouring areas especially housing and commercial areas. When the effluent is discharged it will produce the emission of greenhouse gases such as methane and carbon dioxide to atmosphere and polluting the air quality no matter how effective the method of processing. Therefore, balancing the environmental protection, economic viabilities and sustainable development can be a difficult challenge to the palm oil mill industries.
In Malaysia, there is yet any limitation imposed for odour emission from palm oil mill effluent pond. Plus, there is no proper guideline yet how to reduce the odour. Apart from that, pond cover and anaerobic tank digester have been used widely in many countries such as Thailand and Indonesia in dealing with industrial odour problem. However, the awareness regarding its application in industrial field in Malaysia currently is very low. There is a lack of researches to substantiate the effectiveness of pond cover and tank digester in reducing odour from the palm oil mill effluent.
This research is based on two main objectives, which are:
- To determine the odour emission limit from the Palm Oil Mill Effluent pre-treatment pond
- To determine the odour emission from different anaerobic treatment systems
In this study, three sites have been chosen; Tian Siang (Air Kuning) Sdn. Bhd, Malpolm Industries Sdn. Bhd, and Taclico Co. Sdn Bhd with different types of effluent treatment system. Odour assessment was performed in-situ, using the Scentroid SM100 In-field olfactometer in conjunction with odour intensity and descriptor nearby the open, covered anaerobic pond and tank digester.
In addition to in-field odour assessment, odour samples were also collected from the uncovered ponds and analysed in the USM odour Laboratory within 24 hours. Samples were collected primarily from cooling and acidification pond. Odour concentration will be determined using dynamic olfactometry. Palm Oil mill effluent samples were also collected for each site to determine its Chemical Oxygen Demand (COD), Total Solid (TS), Ammonia and Hydrogen Sulphide.
This research focuses on evaluating the effective of using covered anaerobic that will act as an odour control in reducing the odour level produced by POME and this study also to determine an odour limitation for palm oil mill effluent and at the same time it will helping Department of Environment (DOE) to proposed odour limit for palm oil mill, as well as recognizing odour control techniques for odorous area within a palm oil mill. It is very important to tackle odour pollution resulting from treatment ponds of palm oil mill which almost caused a less comfortable in all areas around the plant.
Therefore, this study aimed to help to reduce the odour resulting from waste treatment ponds of palm oil mill. With the establishment of this odour barrier the problem of odour resulting from the treatment pond plants can be controlled from spreading and almost caused severe odour problems to the neighboring area including villages, residential areas, and institutions. In addition, from this research also could help oil palm industry in forming a way to curb the problem of smell that produce from palm oil mill.
This dissertation is divided into five chapters as a whole. The first chapter describes the background of POME and system to be used for treating odors generated by the POME. The problem statements of why this study is conducted and a description of the objectives of this study is also discussed. In addition, the effects and benefits that can be gained from this study are presented in this chapter.
Next is Chapter Two, which reviews previous studies that have been carried out in connection with this study such as Malaysia palm oil mill, palm oil mill effluent, and effluent treatment.
The next chapter is Chapter Three. This chapter is an important chapter in which it describes in detail how the study was conducted, the methods used, as well as all the equipment involved throughout the study. The experimental procedures, collection of odour sample from the POME sample are also elaborated in this section.
Chapter Four presents all the result obtained and the analysis that have been conducted which include results from the experiments of ammonia test, COD test, sulfide test, total solid test and personal olfactometer test.
The last chapter is Chapter Five. This chapter describes the conclusions of all findings of this study and will show that the objective of this study successfully met. Some suggestions are also proposed in this section to improve the study in the future.
This chapter explains about the treatment of Palm oil mill effluent (POME) and the environmental problem involved in this treatment. One of the highlighted in this chapter is POME odour problem where it reviews the compounds in POME malodour emission and the odour control that have been implemented in the recent years by the palm oil mill industries.
In 2012, Malaysia was recorded as the world’s second largest producer of palm oil with the production of 18.7 million tons of crude palm oil (CPO) (MPOB, 2012). This crude palm oil was produced from 429 palm oil mills located all over Malaysia. Figure 2.1 shows the number of palm oil mills in Malaysia by year, and the trend shows that the number of mills is increasing over the year (Taha and Ibrahim, 2013).
The growth of the palm industries in Malaysia has been phenomenal. From a mere 400 hectare planted in 1920, the hectarage increased to 54000 hectares in 1960 whereas in 2011 the hectarage of palm oil in Malaysia was up to 5 000 109 hectares. Since then, many more areas have been opened for oil palm cultivation, either from jungles, or from the conversions of the plantations that originally supported rubber or other crops (MPOB, 2014). However, while the oil palm industries have been recognized for its contribution towards economic growth and rapid development, it has also contributed to the environmental pollution due to production of huge quantities of by-product from the oil extraction process (Rupani et al., 2010).
Figure 2.1: Number of Mills in Malaysia by Year
(Taha and Ibrahim, 2013)
There are many environmental problems related to POME such as discharging of palm oil mill wastewater without proper treatment will damage the environment by polluting water and causing a foul smell in the neighbourhoods of a factory. According to Hassan et al. (2013) that had conducted a research on POME, this wastewater is viscous brownish liquid and contains substantial quantities of solid which are left after the treatment which are commonly known as POME sludge. Hassan et al. (2013) also stated that due to the large quantity of POME production each year, the amount of sludge increases, respectively that results in bad odour and considered as a pollutant.
Chin et al. (2013) reported in their research that the generations of palm oil mill effluent (POME) together with the production of crude oil have polluting characteristics that create environmental issues for the palm oil in Malaysia. Wu et al. (2010) said that ponding system is the most conventional method implemented for POME treatment in Malaysia due to low operating cost. Yacob et al. (2006) reported that treating POME using ponding and or open digesting tank system produces the emission of greenhouse gases such as methane (CH4) and carbon dioxide (CO2) to the atmosphere and has been recently reported as a source of air pollution from the palm oil mills. Thus, there is an urgent need to find an efficient and practical approach to preserve the environment while maintaining the sustainability of the economy (Lorestani, 2006).
Kun and Abdullah (2013) stated that palm oil wastes such as fiber and shell are used as fuel to generate energy to run the palm oil mill and the utilization of these wastes as boiler fuel is creating a serious emission problem in the industry. The emission are not only posing threat to human health, but also affecting agricultural crops, forest species and ecosystems (Kun and Abdullah, 2013).
The liquid waste generated from the extraction of palm oil of wet process comes mainly from oil room after separator or decanter. This liquid waste combined with the wastes from sterilizer condensate and cooling water is called palm oil mill effluent
(POME) (Salmiati et al., 2010). POME comprises a combination of the wastewaters which are principally generated and discharged from the following major processing operations as follows (Salmiati, 2010):
- Sterilization of FFB – sterilizer condensate is about 36% of total POME or about 0.9 tonnes POME for each produced tonnes of palm crude palm oil.
- Clarification of the extracted crude palm oil (CPO) – clarification wastewater is about 60% of total POME (approximately 1.5 tonnes of sludge obtained per tonnes of produced crude palm oil).
- Hydrocyclone separation of cracked mixture of kernel and shell hydrocyclone wastewater is about 4% of total POME.
The palm industry has contributed significantly towards Malaysia foreign exchange earnings and the increase in standard of living of its population (Yusoff and Hansen, 2007), however the effluent from the industry is known to be an environmental pollutant based on its high compositions of total solids, suspended organic solids, dissolved organic matter among others as represented in Table 2.1. Characteristics of palm oil mill effluent depend on the quality of the raw material and palm oil production process in palm oil mills (Esa et al., 2010).
Other important parameters that were seldom considered in the characterization of POME are as follows total phosphorus (TP), total organic carbon (TOC), total Kjeldahl nitrogen (TKN), lignin and sulfate concentrations, and toxicity (Yong et al., 2010). Yong et al. (2010) also highlighted that these parameters are very vital in determining the suitable treatment method for industrial-scale Waste Water Treatment Plant (WWTP) designs besides detecting the operational problems of the selected treatment system due to the characteristics of POME.
Table 2.1: Characteristics of POME (Poh, Yong and Chong, 2010)
|Parameter||Ahmed et al. (2003)||Najafpour et al.
|Oil and Grease
|Total Solids (mg/L)||40500||–||68854-75327|
|Total Volatile Solids
**All units in mg/L exclude pH
The regulation implemented for wastewater discharge from palm oil industry under Environmental Quality Act (EQA) 1974 [ACT 127] is called the Environmental Quality (Prescribed Premises) (Crude Palm Oil) Regulation 1977 (DOE, 1999). Environmental quality regulations for oil palm industry are become stringent in Malaysia. Effluent standard and effluent charges under licensing system were operated under Malaysia government in the early 90’s (Igwe and Onyegbado, 2007).
Typical parameter limits for wastewater of palm oil mill which stated in Second Schedule of Regulation 12(2) and (3) of Environmental Quality (prescribed Premises) (Crude Palm Oil) Regulations 1977 is shown as Table 2.2 (DOE, 1999). The parameters shown in Table 2.2 are the key point of decision on whether the wastewater is allowed to be discharged into watercourse. For the environmentally sensitive areas in Sabah and Sarawak, for example Kinabatangan River, DOE has stricter the effluent limit for BOD which cannot exceed 20 mg/L since 2006 (Madaki and Seng, 2013a). Effluent charges or penalty will be imposed on industry which has not fulfilled the wastewater discharge standards.
Table 2.2: Effluent Discharge Standards for Wastewater from Palm Oil Mill (DOE, 1999)
|Biochemical oxygen demand||100|
|Chemical oxygen demand||1000*|
|Oil and grease||50|
*No change in discharge standard after 1982 (Aris et al., 2008)
**All units in mg/L exclude pH
Odours can be generated and released from virtually phases of wastewater collection, treatment, and disposal. The potential for the initial release or later development of odours begins at the point of wastewater discharge from homes and industries. Hydrogen sulfide, a major odour source in wastewater treatment systems. Metallic sulfide compounds in wastewater produce a black colour, indicating the presence of dissolved sulfide (Process et al., 2007). Ammonia and organic odours are also common. Effluent had high COD level which means a greater amount of oxidizable organic material reduce the dissolved oxygen (DO) levels. A low level of dissolved oxygen creates anaerobic condition, commonly predominates by anaerobic bacteria and other microbes that produce CH4 and H2S with bad smells (Forman, 2014).
The palm oil industry wastes were generated, first at the oil palm plantations during pruning (fronds), harvesting (fronds), and replanting (trunks). It is generated, second, at the palm oil mills, which includes biogas and biomass.
The oil palm plantations generate huge amounts of waste such as trunks, fronds, empty fruit bunches, shells, and fibers. These wastes comprise biomass in the form of lignocelluloses, which have potential for generating energy, according to Goh et al. (2010). The total area of oil palm cultivation in the year 2007 in Malaysia was 4,304,914 hectares.
Oil palm frond is one of the most abundant agricultural by-products in Malaysia. Almost all pruned fronds are discarded in the plantation, mainly for nutrient recycling and soil conservation. Oil palm frond has great potential for use as a roughage source or as a component in compound feed for ruminants.
Palm oil mill effluent, or POME, is the effluent generated from the final stages of palm oil production in the mill. For every tonne of crude palm oil extracted from milling, about 2.5 tonnes of POME is generated (Sulaiman et al., 2009), and in 2005, about 66.8 million tonnes of POME were produced (Vairappan & Yen, 2008). If it is discharge directly into receiving waterways, it has the pontential to cause adverse environmental consequences. In addition, palm oil mill effluent has a foul smell and can cause odour pollution.
The two major problems associated with air emission are biogas released by POME in the pond during anaerobic digestion and boiler ash. At the milling stage of palm oil production, the boiler is the most significant contributor of air pollutants (Yusoff & Hansen, 2007). The composition of boiler ash is a mix of clinkers and ash. Typically, the Malaysian palm oil mills burn some of the wastes to produce electricity and steam required for sterilization of the fresh fruit bunches (Yusoff, 2006). This is economically efficient but the combustion process of the boiler releases emissions such as particulate matters, CO,
NOx(Ahmad et al., 2004). The biogas is a mixture of mainly methane and carbon dioxide, methane, a greenhouse gas, is 20 times more harmful than carbon dioxide on climate change. The non-recovered biomethane emission from POME contributed the highest impact towards the environment and makes the overall processes not environmentally friendly.
These are two principle sources of air pollution in the mills that are caused by incomplete combustion of the solid waste materials (Thani et al., 1999). The main practice of treating POME is by using ponding and/ or open digesting tank systems (Ma et al., 1999). The emission of greenhouse gases (
CO2from these systems to the atmosphere has been recently reported as a source of air pollution from the palm oil mills (Yacob et al., 2005).
There are many technologies introduced to treat POME. Conventional biological treatments are aerobic digestion, anaerobic digestion as well as combined aerobic anaerobic digestion system. Bioreactor system has also been introduced in POME treatment with its advantages. Anaerobic Expanded Granular Sludge Bed (EGSB) reactors is investigated to achieve the better enhancement on COD removal of POME. Chemical treatments like coagulation-flocculation and membrane separation technologies are also the current treatment for POME. Advantages and disadvantages of anaerobic and alternative treatment method are shown Table 2.3.
Table 2.3: Advantages and Disadvantages between Anaerobic and Alternative
Treatment Methods (Abdulrahman et al., 2013)
||Ahmed et al.,
Metcalf et al.,
||Metcalf et al.,
Borja et al.,
||MA et al., (1997)|
||Doble et al., (2005)|
The raw effluent is treated using a ponding system comprising three phases (i.e., anaerobic, facultative, and algae processes) as shown in Figure 2.2. Although the system takes a longer retention time of 90 days, it is less sensitive to environmental changes, stable, efficient, and could guarantee excellent pollutant biodegradation efficiency of above 95% (APOC, 2011).
Figure 2.2: Stabilization Lagoon (Ponds)
(Palm Oil Mill Effluent Treatment, 2015)
Ponding is a general term which includes waste stabilization lagoons (ponds) and oxidation ponds. The term oxidation pond has also been loosely used and can mean aerobic, facultative, maturation, or sometimes it may even be used for anaerobic pond. Ponding essentially employs a biological method of treatment for wastewaters. It is also used where land space is available. It can achieve a reasonable degree of treatment, is low in construction and operating costs and is easily maintained, as the technology required is relatively unsophisticated. Ponds have been used extensively in several other countries for the treatment of industrial wastewaters amenable to biological treatment (Wong, 1980). The odour from anaerobic pond has been reported by Chotwattanasak and Puetpaiboon (2011) as a nuisance to the neighbouring community.
From the baseline study (Yacob et al., 2006a) of methane emission from anaerobic ponds of POME treatment from two anaerobic ponds in Felda Serting Palm Oil Mill, Negeri Sembilan, Malaysia for 52weeks, the methane content was between 35.0% and 70.0% and biogas flow rate ranged between 0.5 and 2.4 L/min/m³. The total methane emission per anaerobic pond was 1043 kg/day. The total methane emission calculated from the two equations derived from relationships between methane emission and total carbon removal and POME discharge were comparable with field measurement. This study also revealed that anaerobic pond system is more efficient than open digesting tank system for POME treatment.
Modification on conventional treatment is one of solution to improve the quality of POME wastewater discharge, Ismail et al. (2013) introduced the combined system which is conventional ponding system and adsorption as POME treatment in mill. Zeolite was the adsorbent used in adsorption process because it has potential to reduce heavy metal. A significant reduction in BOD concentration, heavy metals and turbidity in POME has resulted under adsorption treatment.
Bioreacter or tank system is also applied in palm oil industry nowadays in order to capture the biogas for electric energy production. It has advantages such as less land is required, short HRT and more environmentally sound (Narasimhulu and Nanganuru, 2010). Wang et al, (2015) treated POME using anaerobic expanded granular sludge bed (EGSB) reactors and about 94.89% COD removal was achieved with 3587 mg/L COD of effluent. Another research was hybrid up-flow anaerobic sludge blanket (HUASB) reactor equipped with anaerobic filter and removed up to 97% COD of POME (Badroldin, 2010).
POME generated through oil extraction processes has a great impact to the industry. Owing to its chemical properties and volume of discharge, a large wastewater treatment is required to reduce the polluting strength of POME, before safe discharge. Thus, the selection and performance of the treatment system determine the quality of wastewater discharged. A simple and innovative bioreactor process that is capable of treating POME efficiently is superior to the conventional system, as it operates with very short hydraulic retention times, takes high organic loading, requires less space, and is more environmentally friendly.
500 m³ closed digester was constructed to evaluate the POME treatment efficiency for a comparison study with open digester system a Felda Serting Hilir, Negeri Sembilan, Malaysia. Prior to actual treatment, the closed digester was subjected to a start-up operation, which is crucial to the overall POME treatment. During the start-up operation, the system demonstrated a remarkable performance of high COD removal efficiency (up to 97%) and satisfactory ratio of volatile fatty acid:alkalinity (VFA:Alk) between 0.1 and 0.3. The lowest hydraulic retention time (HRT) at 17 days was achieved in less than 3 months. Initial biogas production rate was high, however it declined during higher organic loading rates (OLR). This was attributed so sudden variations of POME chemical properties that affect the system stability. The start-up strategy used for this process has achieved its objectives by creating an active microbial population which was expressed in terms of key performance parameters such as % COD removal efficiency, pH, VFA:Alk, and HRT (Yacob et al., 2006b).
In most cases, odours from anaerobic pond created by incomplete anaerobic break-down of the organic manure. Anaerobic break-down occurs in the absence of free oxygen and uses microorganisms that thrive in these conditions. Aerobic breakdown can occur if there is sufficient oxygen to support aerobic microorganisms. Aerobic breakdown produces more CO2 and less CH4 than anaerobic digestion. Generally, aerobic digestion does not produce the offensive odours associated with incomplete anaerobic break-down (FSA Environment, 2000).
Generally, the treatment system for POME are operated on two-phase anaerobic digestion process followed by natural aeration process. This two-phase anaerobic process gives excellent pollutant destruction efficiency of above 95%, while natural aeration ensures that the final pollutant levels in the effluent are within the limits set by Department of Environment (DOE). Anaerobic digestion occurs when organic material is broken down by bacteria in four major processes: hydrolysis, acidogenesis, acetogenesism and methanogenesis. Hydrolysis is the process in which carbohydrate, proteins, fats are converted to sugars, fatty acid and amino acids. Acidogenesis is the process in which the sugars, fatty acids, and amino acids are converted to carbon dioxide, ammonia, and acids, Acetogensis is the process which creates acetic acid and carbon dioxide. The final process, methanogenesis is when biogas is formed. Biogas contains a mixture methane and carbon dioxide gases. The volatile acids are then converted into methane and carbon dioxide (APOC, 2011). Figure 2.3 show the anaerobic digestion processes.
The advantages of anaerobic digestion system are:
- The two phase system allows greater control of digester environmental conditions
- Long solid retention times allow better biodegradation efficiencies
- Additional settling of liquor ensures minimum loading to the aerobic process
- There is capability to cope with full effluent load, regardless of fluctuation
Figure 2.3: Anaerobic Digestion phase (Khanal, 2008)
Odorous compounds include organic or inorganic molecules. The two major inorganic odors are hydrogen sulfide and ammonia. Hydrogen sulfide is the most common odorous gas found in wastewater collection and treatment systems. Its characteristic rotten-egg odour is well known. The gas is corrosive, toxic, and soluble in wastewater. Ammonia also sources of malodour and its characteristic sharp, and pungent. Nagata, Y. (2003) stated that the odour threshold of ammonia is 1.5ppm and for hydrogen sulfide is 0.00041ppm.
Bio degradation processes in ponds depend primarily on the aerobic or anaerobic microbial activity. Odour is largely a result of this microbial activity due to the biological nature of the process, a large number of factors affect odour emission from effluent ponds. The main factors include:
- Loading rate;
- Start-up conditions;
- pH; and
- purple Sulphur bacteria
188.8.131.52. Loading Rate
The loading rate of an effluent pond system is expressed as the mass of volatile solids per cubic meters of pond volume added per day. It has a major impact on the amount of odour that is generated from the system. Several field studies have shown a clear relationship between loading rate and odour emissions. Chastain & Henry (1999) indicated that at high loading rates (i.e. 480 g VS/m³day), significant odour will produced near the pond 80 % of the time. If loading rate is reduced to 30 g VS/m
³day, the odour will be insignificant. This suggests that one way to control odour is to use a very small loading rate.
There are three major temperature ranges in the anaerobic digestion processes. Psychrophilic is operated below 25ºC, mesophilic range is between 25ºC to 40ºC and the optimum is at 30ºC to 35ºC. The thermophilic is operated at temperature greater than 45 ºC (El-Mashad et al., 2004). The main contributions of the thermophilic anaerobic process are higher stability for solids reduction, higher biogas production improvement of the energy balance of the treatment plant, high resistance to foaming, less odour and high effect of destroying pathogens in the thermophilic digesters (Zábranská et al., 2002). One of the imperative parameter to anaerobic treatment is operating temperature that selects the dominant bacterial flora and determines microbial growth rate (Patel and Mandawar, 2002). Biogas production from the thermophilic anaerobic digestion treating fruit and vegetable wastes was higher on average than psychrophilic and mesophilic by 144% and 41% respectively (Bouallagui et al., 2004). Temperature- phased anaerobic digester was developed with combination of mesophilic and thermophilic process to enchance the treatment performance.
A new pond should be filled to 50 percent of its permanent volume with liquid before manure loading begins. Start-up during warm weather and seeding with bottom sludge from a working pond will speed establishment of a stable bacterial population. Manure should be added to anaerobic ponds in a regular stream without ‘shock’ loadings, which can cause sharp increases in odour production and wide fluctuations in nutrient content. Liquid levels should not be allowed to fall below the design treatment level, so that adequate pond volume is maintained for optimum bacterial digestion (NCSU, 1998).
An anaerobic pond that is operating properly will have a pH ranging from 7 to 8 (Tchobanoglus & Burton, 1991). When the anaerobic pond is operated properly, the biochemical reactions will maintain the pH in the proper range. If imbalance develops, the acid forming bacteria exceed the methane formers causing a build-up of volatile acids in the pond. If this continues, the buffer capacity is exceed causing the pH to drop below 6.0. Under this condition, the anaerobic ponds start to produce odours.
pH has a strong interaction with the concentration of volatile organic acids. The lowest pH values occur when the volatile organic acids are at maximum concentration. The pH in new ponds without adequate dilution water or in overloaded ponds can be reduced to 6.5 or less (acidic), thereby causing odour problem.
Main ponds exhibit a purple colour in the liquid, caused by naturally occurring purple Sulphur bacteria. These are phototropic organisms that oxidise sulphide under anaerobic conditions. When these organisms are dominant, pond odour, ammonium nitrogen and soluble phosphorous are reduced. The purple colour is a good indicator of a pond working at its optimum (NCSU, 1998).
To encourage desirable purple sulfur bacteria, the first factor is proper pond size in terms of the amount of manure produced. Ponds with small permanent pools often tend to produce odour because they are too small to adequately handle wastewater. Pond with a large permanent pool have less odour problems.
Industrial odours are a major environmental problem. Emissions of many odorous compound are produced from biological activities or chemical processes. Most of the odorous substances derived from anaerobic decomposition of organic matter contain sulfur and nitrogen (Bhawan et al., 2008). These malodourous compounds can create an unpleasant working environment, which is obviously a concern to those who are working there and the residents who live near industrial premises.
Many techniques have been applied to manage odour pollution. Table 2.4 below displays the summary of odourous air treatment which is commonly implemented in the industrial field.
Table 2.4: Summary of Odorous Air Treatment Alternatives
(Water Environment Federation, MOP-22, 1995)
|Technique||Frequency of Use||Cost Factors||Advantages||Disadvantages|
|High||Moderate capital and O&M cost||Effective and reliable, long track record||High chemical consumption, not effective for VOCs|
|Fine-mist wet scrubber||Medium||Higher capital cost than packed towers||Lower chemical
consumption, can be design for VOC removal
|Water softening required for scrubber water, larger scrubber vessel|
|Activated carbon absorbers||High||Cost effectiveness depends on
frequency of carbon replacement
|Simple, few moving part||Only applicable for relatively dilute air stream in order to
ensure long carbon
|Bio-filters||Medium||Low capital costs||Simple, minimal
|Effective with a range of odours,
requires monitoring for bed moisture, required periodic media replacement
|Thermal oxidizers||Low||Very high capital cost||Highly effective for
VOCs and odour
|Only economical for high-strength,
difficult to treat air streams
|Diffusion into activated sludge basins||Low||Economical if existing blowers diffusers are used||Simple, low energy, effective||Concern for blower corrosion, may not be appropriate for very strong odour|
|Odour masking agents||High||Cost depends on chemical usage||Low capital cost, easy to obtain||Only mask odours, no VOC control|
Emission of odour from liquid sludge occurs by volatilization. Volatilization or evaporation of chemical substance in water is influenced by air temperature and humidity, and wind speed, and turbulence in the water body (Berkeley; and King, 1981). Oxygen is present in the upper portions of pond, so aerobic processes occur here. There is no oxygen present in the lower levels of the pond, so the processes here are anaerobic. Oxygen is added to the water in two ways. The wind and the surface area prompt oxygen to diffuse into the water from the air. Algae also produce oxygen during photosynthesis when the sun is present. The oxygen is then used up by bacteria in the aerobic portion of the pond. These bacteria use oxygen to break down organic matter suspended in the water. In turn, the bacteria produce the carbon dioxide which the algae use in photosynthesis. Some of the solid settle to the bottom of the pond. These solids are broken down by anaerobic bacteria which produce methane or hydrogen sulfide. Figure 2.4 show odour volatilization.
Figure 2.4: Odour volatilization
(Lagoon Design and Construction, 2010)
This odour emission must be control, therefore impermeable cover (that collect methane and odorous gases) have potential for odour reduction. The collected gas can be flared or use to generate power. However, as an odour control method only, the cost of durable, permanent lagoon covers may limit their use (FSA Environmental, 2000).
Covered are very effective method of reducing odour release from manure storage structures. A covered storage structure produces less odours as wind no longer passes over the surface of the slurry and, when equipped with a flare to combust the biogas, further reduces objectionable odours and harmful gases such as VOCs, H2S, volatile fatty acids, and NH3 (Bicudo et al. 2004, USEPA 2006).
Most impermeable cover can be expected to reduce odours by 80-95%. Permeable covers provide a lower cost alternative to impermeable covers. Permeable covers typically have a much shorter lifespan than impermeable covers. Materials that have successfully been used as permeable covers include straw, cornstalks, light weight caly balls, geotextile materials and ground rubber. Permeable covers reduce odour by sheltering the manure surface from air as well as providing an aerobic layer over the manure that can remove some odour as it passes through (Bicudo et al., 2004)
Guaruino et al. (2006) reported using permeable covering system will be reducing reductions of NH3 emissions from swine and dairy slurry in the range of 60-100% with 140-mm solid covers or 9-mm liquid covers. Miner et al. (2003) reported that a permeable polyethylene form lagoon covered reduced NH3 emissions by approximately 80% on an anaerobic swine lagoon. Comparison of odour reduction by using different type of cover are show in Table 2.5
Table 2.5: Comparison of odour reduction using different type of cover (Nicolai et al., 2004)
|Cover Type||Material||Odour reduction (%)|
|Permeable||Biocover (8 to 12 in)||40 to 80|
|Geotextile||40 to 65|
|Geotextile + 8 in Biocover||69 to 78|
|Impermeable||Floating Plastic (HPDE)||60 to 95|
|Inflatable Plastic Dome||95|
In an anaerobic digestion system, a tank holds the manure while anaerobic digestion anaerobic bacteria break it down, releasing anaerobic gases (methane, ammonia, hydrogen sulfide, carbon dioxide). The digester size is based on the detention time and the pounds of volatile solids. Anaerobic digester are very effective at controlling odour, nearly eliminating them from associated manure storage structure. Odours remain within the sealed digester during biodegradation (FSA Environmental, 2000). When the biologically-stabilized liquid and solids are transferred to the storage pit they produce very little odour. Very thick manure might require dilution ahead of the digester. From the tank digester, it will be produce biogas and this generates electricity for sale to the local grid. This system is expensive and complex but eliminated odour and has the potential to generate income from sales of electricity and fertiliser.
There are many different commercial products that claim to reduce odours from anaerobic pond. In most cases, there are either been no scientific testing of the products or the scientific tests have been inconclusive. Although some piggery operators are convinced of their effectiveness, there is not sufficient data to justify their recommendation as an odour control option. Most of the product are found in one of the following categories (Swine Odor Task Force 1995):
- Masking agents are mixtures of aromatic oils used to cover an objectionable odour with a more desirable one.
- Counteractants are aromatic oils that cancel or neutralise an odour so that the intensity of the mixture is less than that of it constituents.
- Digestive deodorants contain bacteria or enzymes that eliminate odours through biochemical digestive processes. For example, sarsaponin promotes microbial action.
- Adsorbents are products with a large surface area that adsorb the odours before they are released to the environment. Sphagnum peat moss, for example, has reduced odour for some lagoons.
- Chemical deodorants are strong oxidising agents or germicides. Germicides such as orthodichlorobenzene chlorine, formaldehyde, and paraformaldehyde alter or eliminate bacterial action responsible for odour production.
Misting system is a series of mist produced by nozzles that are installed around the perimeter of an area as shown in Figure 2.5. Misting system will be well-equipped if the component such as tubing, special nozzles, and appropriate pumping systems are included. Some additional components will be required to improve misting system’s performance for a more specific use.
Figure 2.5: Perimeter Misting System
Misting system able to create fine mist which is more effective with minimal use of water and electricity (Bhawan et al., 2008). Nowadays, the application of misting system has an important role in dealing with environmental problems especially for the purpose of cooling, odour control, and dust control. Water mist has been the subject of extensive research and development previously, resulting in system that have been optimized and proven for some application including odour control (Williams et al., 2006). For odour problem to exist it must be generated, transported and received. Jefferson (2004) reported that the polluted and odorous gas emissions can also be treated using the misting system whether for the purpose of masking or eliminating of odour and one of the mechanisms to reduce odour is spraying some products that are supposed to mask or neutralize the odorous compounds.
The odour emission from the palm oil mill has been recognized as nuisance to the surrounding areas especially to the surrounding community. According to the previous researches, hydrogen sulfide H2S and ammonia NH3 are the odourous compounds contributing to the strong offensive smell of generated from the anaerobic treatment of effluent. Besides that, previous researches also show that covered and tank anaerobic lagoon can reduce the odour and methane gas but for Palm oil mill effluent the effectiveness of these cover and tank digester in controlling odour is not yet validated.
Thus, it is important to work on the efforts in reducing this malodour. A study is required to address this knowledge especially in the management of odour from palm oil mills.
The surrounding odour level affected by POME odour emission were measured on-site using Portable Personal Olfactometer (SM100) next to anaerobic pond at Taclico, anaerobic cover pond at Malpom and anaerobic tank digester at Tian Siang. For all sites, odour samples were collected using flux chamber and vacuum chamber at the cooling pond and brought to lab for dynamic olfactormetry analysis.
There are yet no instrument-based methods that can measure an odour response in the same way as the human nose except in some trials at the level of laboratory research. Therefore, dynamic olfactometry is typically used as the basis of odour management. Dynamic olfactometry is the measurement of odour by presenting a sample of odourous air to a panel of people at a range of dilutions and seeking responses from the panellists on whether they can detect the odour. The correlations between the know dilution ratios and the panellists’ responses were then used to calculate the number of dilution of the original sample required to achieve the odour detection threshold (WA DEP, 2002)
Odour concentration measured by olfactometry is expressed as odour units per cubic meter (OU/m³). Odour unit were defined as the volume of diluent required to dilute a unit volume of odour unit until the detection threshold of the odour was obtained (Schmidt, 2002). Alternatively, odour unit per cubic meter were defined as the concentration of odour in one cubic meter of air at the panel detection threshold of the odour (NCMAWM, 2001: CEN, 1999).
Sensory filled odour assessments using in-field olfactometer are useful for area and boundary investigation as well as for following up odour complaints and tracking odour sources, as shown in Figure 3.5. The Scentroid SM100 in-field olfactometer incorporates a dilution device within a portable device, allowing direct measurement of odour concentration to be carried out in real time in the field. Odour assessment was performed in-situ, using the Scentroid SM100 in-field olfactometer in conjunction with odour intensity and descriptor for a total of 12 samples nearby the covered/uncovered anaerobic lagoons. The odour concentration detection range for this SM100 is 3.5 OU/m³ until 11,355 OU/m³.
Figure 3.5: SM 100 Portable Personal Olfactometer
Odour intensity is another measure of the strength of an odour (Zhang et al., 2002). However, unlike odour concentration, it is a measure of the human response to an undiluted odour (Hamilton & Arogo, 1999). A common way of measuring odour intensity is to compare the intensity of an odour the intensities of different but known concentrations of a reference odorant. It is recommended that successive concentrations of the reference odorant are greater than the preceding levels by a factor of two (ASTM, 1999).
Odour intensity is obtained when a match is found between the intensity of odour and the intensity of one if the concentration of the reference odorant. It is often difficult to match the intensity of an odour to the intensity of only one concentration of reference odorant. The German standard VDI 3882 provides qualitative descriptions of odour intensity with a numerical scale that may be used in back-calculating the corresponding odour concentration, these descriptions are shown in Table 3.1 (VDI, 1992). Like odour threshold determination, assessment of odour intensity is undertaken in the laboratory by odour panels and dynamic olfactometry equipment. Panel members presented with odour at concentrations greater than the odour threshold (by definition 1 OU/m
³) and asked to rate the odour strength on the scale in Table 3.1 (WA DEP, 2002).
Table 3.1: Odour intensity categories.
|Odour strength||Intensity level|
The specific character of an odour can be defined based on its quality classification which can be expressed in terms of ‘descriptors’. The odour descriptors wheel was used to describe the odour quality. Based on this odour wheel in Figure 3.6, there are 8 categories of odour quality such as floral, fruity, vegetable, earthy, offensive, fishy, chemical, and medicinal.
Figure 3.6: Odours Descriptor Wheel (Mc Ginley et al., 2002
For this study, flux hood chamber had been using for odour sampling at cooling pond. The isolation flux hood (chamber) method was developed by the USEPA in 1983 (Klenbusch, 1986). The flux hood system has been used for nitrous oxide emissions from farmland (Denmead, 1979), measurement of gaseous emission rate from land surface (Klenbusch, 1986) and sampling emissions from hazardous waste dumps (Clark et al., 1988). For odour sampling it is important that the equipment used to collect an odour sample does no contaminate the sample or cause minimal changes to the odour in the sample. Therefore, specialised equipment and materials are required. Sample are collected into special purpose plastic bags made of TedlarTM, Nalophan or Polytetrafluoroethylene (PTFE) to minimise adsorption of the odour onto the bag surface (Freeman et al., 2000).
184.108.40.206. Odour Sample Collection
Laboratory olfactometry often is a part of or follows field odour investigation and studies. It is useful for identification of strength of odour emission of a source and in design of odour control system. Odorous air sample was collected from a palm oil mill effluent pond using a flux chamber and 10 L Nalophan bag for transport to the odour testing laboratory. Odour samples were collected from the uncovered palm oil mil effluent ponds and analysed in the USM odour Laboratory within 24 hours. Samples were collected primarily from the cooling pond and acidification pond. Odour sampling and assessment was performed according to MS 1963 2007 Air Quality- determination of odour concentration by dynamic olfactometry. Figure 3.7 show flux hood and vacuum chamber being used for odour sampling.
Figure 3.7: Flux chamber and Vacuum chamber for odour sampling
220.127.116.11. Determination of odour concentration (OU/m³)
A Dynamic olfactometer Scentroid SS400 (IDES Canada) is a device that uses a dynamic odour dilution system. An odorous air stream is continuously diluted with an odour-free air stream using various flow meters and gauges. The diluted odorous air is presented to a number of panellists. The operator presents a series of different odour/odour free air dilutions to the panellists who are situated in an odour-free environment (Watts, 1999a).
Odour concentration is determined by finding the dilutions to threshold. This is defined as the dilution of the original odour sample at which half the panel can just detect the odour. The dilutions to threshold is found by presenting the panel with a series of dilutions of the sample. These dilutions should cover the range from where none of the panel detects the odour to where all panellists detect the odour. The procedure allows determination of the perception curve (DNI, 1990), that is the relationship between dilution and the percentage of the panel that correctly detects the odour.
18.104.22.168. Determination of
in odour sample
In addition, same sample has been used for ammonia and hydrogen sulfide test using Scentroid OdoTracker TR8. The Scentroid OdoTracker is wearable multi-sensor that measures Hydrogen Sulfide and Ammonia in ppm level. Figure 3.4 shows that OdoTracker TR8 has been used in this study.
Conducting Ammonia test is important to identify the ammonia content in POME since ammonia is one of the main sources of malodour and pollutant that produced by POME. . Sulfide test is important to identify the Sulfide content in POME that will converted to hydrogen sulfide. Hydrogen sulfide can come from different sources. Volatile sulfur compounds as shown in Figure 3.8 shows the sources of Hydrogen sulphide where sulfur content is converted to sulfide. This condition occurs naturally in crude petroleum and natural gas, and can be produced by the breakdown of organic matter and human/ animal wastes such as sewage (CCOHS, 2012). This source also stated that it can also be produced by sulfur bacteria or chemical reactions resulting from pollution. Sulfur, S has a sharp, offensive odour (Sulfur, 2016) and sufficient sulfur is normally available in domestic wastewater in the form of organic sulfides for the production of odorous gases by anaerobic and facultative bacteria (Edwards et al., 2008). Hydrogen sulfide is an S-containing compound that has a rotten-egg smell.
Figure 3.8: Sources of Hydrogen Sulfide (Angela, 2005)
POME samples used for this experiment were taken at the anaerobic pond from Taclico and Tian Siang Palm Oil industries as shown in Figure 3.9.
Figure 3.9: Anaerobic Pond at Malpom Palm Oil Industries
For every visit to the site, 1 liter of POME was collected in 5 liter HDPE bottles. An amount of 5 liter of POME was required for every experimental run. The rest of the collected POME was stored inside the cool room in Environmental Lab 1 to maintain in its original conditions for further use.
The substances that give rise to the diffusion of odours in areas surrounding a production plant can consist of product of an inorganic nature or volatile organic compounds (Agostinelli, 2005). The odourous compounds generally present in the emissions can be easily identified. The principal compounds, by class of substances possessing odourous characteristics generally identifiable in the various emissions, as deduced from various publications.
Chemical Oxygen Demand (COD) test is the measure of the solution capacity to consume oxygen during the decomposition of organic matter. Under the strong oxidizing agent like acid condition, most of the organic compounds can be oxidized (Belgiorno, 2013). Thus, the COD test was conducted to measure the amount of organic pollutant in the POME samples.
The COD laboratory test was done with combination of COD Digestion Reagent and also COD Acid Reagent. Digestion reagent is combination of few chemicals, which is Potassium Dichromate, Sulphuric Acid, Mercury Sulphate and distilled water. While for acid reagent is combinations of Silver Sulphate and Sulphuric Acid.
The POME sample was diluted before it was tested to bring the results in range. 1 ml of POME sample was measured and poured into 100 ml beaker. Deionized water was added until it reached 100 ml volume. Now the POME sample was ready to be used and a 2.5 ml of that volume was poured into 2.5 ml vial. After that, the sample was mixed with COD digestion reagent and COD acid reagent. Then, the sample was heated at 110 ºC for 2 hours and cooled down to room temperature in about one hour. The COD value measured was using the DR2800 Hach Spectrophotometer with range 3-150 mg/L.
Firstly, the POME sample needs to be diluted as done in the COD test. 1 ml of POME sample was measured and poured into 100 ml beaker. Deionized water was added until it reached 100 ml volume. Now the POME sample was ready to be used and a 25 ml of that volume was poured into measuring cylinder.
Ammonia was measured using DR2800 Hach Spectrophotometer according to the Nessler method. About 25 ml of sample was mixed with 3 drops of Mineral Stabilizer, 3 drops of Polyvinyl Alcohol Dispersing agent and 1 ml Nessler Reagent.
Then the sample was transferred into 10 ml vials and ammonia value taken using the Hach Spectrophotometer, method number 380 (Nessler method) with detection range
2.50 mg/L. Conducting Ammonia test is important to identify the ammonia content in POME since ammonia is one of the main sources of malodour and pollutant that produced by POME.
Firstly, the POME sample needs to be diluted as done in the COD and Ammonia test. The POME sample was diluted before it was tested to obtain result in the range. 1 ml of POME sample was measured and poured into 100 ml beaker. Deionized water was added until it reached 100 ml volume. Now the POME sample was ready to be used and a 10 ml of that volume was poured into vial.
Next, 0.5 ml of Sulfide 1 Reagent and 0.5 ml of Sulfide 2 Reagent were added into the vial. The vial was swirled after each addition. Then the sulfide content of the sample was measured using DR2800 Hach Spectrophotometer, method number 690 (methylene blue method) with detection range 800 µg/L. Sulfide test is important to identify the Sulfide content in POME that will converted to hydrogen sulfide.
This test was referred to method 2540 B (APHA, 2012). A crucible was dry in an oven at 104ºC for one hour and then the crucible will be cool in a desiccator and has been a weight on an analytical balance to the nearest 0.1 mg. Next, 50ml sample has been pour into the crucible and will evaporate the contents to dryness on the steam bath. After that, the crucible will be heated in the oven at 104ºC about 30 minutes to get a constant weight. The crucible has been cool in a desiccator and will be weight.
All data collected was processed for further analysis. For odour sampling, the data odour samples had been diluted and had been analysed using dynamic olfactometer for odour concentration and using TR8 Odotracker for ammonia and hydrogen sulfide in gas content. Then, the data of odour concentration used to plot the box plot graph by using Microsoft Excel 2013 and determine the odour limit for palm oil mill effluent. After that, compared the relationship between odour concentration, hydrogen sulfide and ammonia concentration in gas.
As for the data from SM100, the data collected by the operator need to be converted into concentration value by using Table 3.2. After that, used the data to plot box plot by using Microsoft Excel 2013. For odour intensity, from the percentage of the intensity level that had been calculated pie chart were plotted. Besides that, the specific odour type or characterization that had been noted down by the assessor also will be analysed. Determination of the main cause of the odour episode can be detected from this analysis.
Table 3.2: Scentroid SM-100 Calibration (IDES Canada)