Development of anaerobic digestion methods for palm oil mill effluent (POME) treatment

Microbial community dynamics and functional potentials in the conversion of oil palm wastes into biomethane

Oil palm processing generates substantial waste materials rich in organic content, posing various environmental challenges. Anaerobic digestion (AD), particularly for palm oil mill effluent (POME), offers a sustainable solution, by converting waste into valuable biomethane for thermal energy or electricity generation. The synergistic activities of the AD microbiota directly affect the biomethane production, and the microbial community involved in biomethane production in POME anaerobic digestion has been reported. The composition of bacterial and archaeal communities varies under different substrate and physicochemical conditions. This review discusses the characteristics of POME, explores the microbial members engaged in each stage of AD, and elucidates the impacts of substrate and physicochemical conditions on the microbial community dynamics, with a specific focus on POME. Finally, the review outlines current research needs and provides future perspectives on optimizing the microbial communities for enhanced biomethane production from oil palm wastes.

Microbial granules on reactors performance during organic butyrate digestion: clean production

This critical review for anaerobic degradation of complex organic compounds like butyrate using reactors has been enormously applied for biogas production. Biogas production rate has a great impact on: reactor granulation methanogenesis, nutrient content, shear velocity, organic loading and loss of nutrients taking place in the reactor continuously. Various technologies have been applied to closed anaerobic reactors to improve biogas production and treatment efficiency. Recent reviews showed that the application of closed anaerobic reactors can accelerate the degradation of organics like volatile fatty acid-butyrate and affect microbial biofilm formation by increasing the number of methanogens and increase methane production 16.5 L-1 CH4 L-1 POME-1. The closed anaerobic reactors with stable microbial biofilm and established organic load were responsible for the improvement of the reactor and methane production. The technology mentioned in this review can be used to monitor biogas concentration, which directly correlates to organic concentrations. This review attempts to evaluate interactions among the: degradation of organics, closed anaerobic reactors system, and microbial granules. This article provides a useful picture for the improvement of the degradation of organic butyrate for COD removal, biogas and methane production in an anaerobic closed reactor.

Assessing efficiency and economic viability in treating leachates emanating from the municipal landfill site at Gazipur, India

The leachates emanating from the landfills are high in organic loads and thus become potential sources of contamination for both surface and groundwater. As the landfill ages, the nature of leachate changes from acidic to alkaline. The change in pH level affects the chemical oxygen demand (COD)/biochemical oxygen demand (BOD) ratio and when it is less than 0.63, chemical treatments are more effective over the biological treatment methods such as upflow anaerobic sludge blankets (UASB). The existing literature suggests coagulation-flocculation and advanced oxidation process (Fenton) as effective methods for treating wastewater but no comparison of the two are available. Thus, the present study attempts to identify the most efficient coagulants out of ferric chloride (FeCl₃), ferrous sulphate (FeSO₄) and alum [Al₂(SO₄)₃]. Ferric chloride leading to 99% colour removal, 98% COD removal, 99% decrease in total organic carbon, 94.3% removal in NH₃-N and 91.4% removal in total Kjeldahl nitrogen is observed to be the most efficient coagulant and surprisingly, proves to be even better than Fenton. To understand the field applicability of the two treatment procedures, coagulation with FeCl₃ and Fenton are compared with the UASB method which is currently employed at Gazipur landfill site, Delhi. With lesser operational cost than UASB, both FeCl₃ and Fenton perform better on cost-efficiency scale. Switching from in-suit UASB method to the FeCl₃ method of treatment may result in decreasing the operational cost by 71.9% and to conventional Fenton may result in decreasing the operational cost by 76.8%.

Agro-Industrial Wastewaters for Algal Biomass Production, Bio-Based Products, and Biofuels in a Circular Bioeconomy

Recycling bioresources is the only way to sustainably meet a growing world population’s food and energy needs. One of the ways to do so is by using agro-industry wastewater to cultivate microalgae. While the industrial production of microalgae requires large volumes of water, existing agro-industry processes generate large volumes of wastewater with eutrophicating nutrients and organic carbon that must be removed before recycling the water back into the environment. Coupling these two processes can benefit the flourishing microalgal industry, which requires water, and the agro-industry, which could gain extra revenue by converting a waste stream into a bioproduct. Microalgal biomass can be used to produce energy, nutritional biomass, and specialty products. However, there are challenges to establishing stable and circular processes, from microalgae selection and adaptation to pretreating and reclaiming energy from residues. This review discusses the potential of agro-industry residues for microalgal production, with a particular interest in the composition and the use of important primary (raw) and secondary (digestate) effluents generated in large volumes: sugarcane vinasse, palm oil mill effluent, cassava processing waster, abattoir wastewater, dairy processing wastewater, and aquaculture wastewater. It also overviews recent examples of microalgae production in residues and aspects of process integration and possible products, avoiding xenobiotics and heavy metal recycling. As virtually all agro-industries have boilers emitting CO2 that microalgae can use, and many industries could benefit from anaerobic digestion to reclaim energy from the effluents before microalgal cultivation, the use of gaseous effluents is also discussed in the text.

Preparation and modification methods of defective titanium dioxide-based nanoparticles for photocatalytic wastewater treatment-a comprehensive review

The rapid population growth and industrial expansion worldwide have created serious water contamination concerns. To curb the pollution issue, it has become imperative to use a versatile material for the treatment. Titanium dioxide (TiO₂) has been recognized as the most-studied nanoparticle in various fields of science and engineering due to its availability, low cost, efficiency, and other fascinating properties with a wide range of applications in modern technology. Recent studies revealed the photocatalytic activity of the material for the treatment of industrial effluents to promote environmental sustainability. With the wide band gap energy of 3.2 eV, TiO₂ can be activated under UV light; thus, many strategies have been proposed to extend its photoabsorption to the visible light region. In what follows, this has generated increasing attention to study its characteristics and structural modifications in different forms for photocatalytic applications. The present review provides an insight into the understanding of the synthesis methods of TiO₂, the current progress in the treatment techniques for the degradation of wide environmental pollutants employing modified TiO₂ nanoparticles, and the factors affecting its photocatalytic activities. Further, recent developments in using titania for practical applications, the approach for designing novel nanomaterials, and the prospects and opportunities in this exciting area have been discussed.

Reduction in Free Fatty Acid Concentration in Sludge Palm Oil Using Heterogeneous and Homogeneous Catalysis: Process Optimization, and Reusable Heterogeneous Catalysts

Acid catalysts including Amberlyst 15 and sulfuric acid were used for heterogeneous and homogeneous catalyst reactions respectively, to reduce high free fatty acid (FFA) in sludge palm oil (SPO) using an esterification process. The goal of this research was to reduce high FFA content in SPO to less than 1 wt.% FFA so that it can be employed as a raw material in a transesterification process to produce biodiesel. Amberlyst 15 is an eco-friendly catalyst with many benefits, such as being reusable and generating non-toxic waste after reactions, compared to homogeneous catalysts, although the reaction time of the homogeneous catalyst was faster than the heterogeneous catalytic reaction. Therefore, esterification reactions with a heterogeneous and homogeneous catalytic reaction were carried out to examine conversion of FFA. The heterogeneous catalytic reaction decreased the FFA content from 89.16 wt.% to 1.26 wt.% under the recommended conditions of 44.7 wt.% methanol, 38.6 wt.% Amberlyst 15 catalyst loading, and 360 min reaction time. For homogeneous catalytic reaction, the FFA content of 1.03 wt.% was achieved under the recommended conditions of 58.4 wt.% methanol, 16.8 wt.% sulfuric acid, and 79.7 min reaction time. Furthermore, the results of the reusability research demonstrate that the heterogeneous catalyst may be reused for at least nine cycles. This research showed the promising potential of using SPO non-edible oil for biodiesel production by employing an eco-friendly heterogeneous catalyst for cost-effective environmental remediation.

Anaerobic treatment of ultrasound pretreated palm oil mill effluent (POME): microbial diversity and enhancement of biogas production

In this study, palm oil mill effluent (POME) treated by ultrasonication at optimum conditions (sonication power: 0.88 W/mL, sonication duration: 16.2 min and total solids: 6% w/v) obtained from a previous study was anaerobically digested at different hydraulic retention times (HRTs). The reactor biomass was subjected to metagenomic study to investigate the impact on the anaerobic community dynamics. Experiments were conducted in two 5 L continuously stirred fill-and-draw reactors R1 and R2 operated at 30 ± 2 °C. Reactor R1 serving as control reactor was fed with unsonicated POME with HRT of 15 and 20 days (R1-15 and R1-20), whereas reactor R2 was fed with sonicated POME with the same HRTs (R2-15 and R2-20). The most distinct archaea community shift was observed among Methanosaeta (R1-15: 26.6%, R2-15: 34.4%) and Methanobacterium (R1-15: 7.4%, R2-15: 3.2%). The genus Methanosaeta was identified from all reactors with the highest abundance from the reactors R2. Mean daily biogas production was 6.79 L from R2-15 and 4.5 L from R1-15, with relative methane gas abundance of 85% and 73%, respectively. Knowledge of anaerobic community dynamics allows process optimization for maximum biogas production.

Palm oil industrial wastes as a promising feedstock for biohydrogen production: A comprehensive review

By the year 2050, it is estimated that the demand for palm oil is expected to reach an enormous amount of 240 Mt. With a huge demand in the future for palm oil, it is expected that oil palm by-products will rise with the increasing demand. This represents a golden opportunity for sustainable biohydrogen production using oil palm biomass and palm oil mill effluent (POME) as the renewable feedstock. Among the different biological methods for biohydrogen production, dark fermentation and photo-fermentation have been widely studied for their potential to produce biohydrogen by using various waste materials as feedstock, including POME and oil palm biomass. However, the complex structure of oil palm biomass and POME, such as the lignocellulosic composition, limits fermentable substrate available for conversion to biohydrogen. Therefore, proper pre-treatment and suitable process conditions are crucial for effective biohydrogen generation from these feedstocks. In this review, the characteristics of palm oil industrial waste, the process used for biohydrogen production using palm oil industrial waste, their pros and cons, and the influence of various factors have been discussed, as well as a comparison between studies in terms of types of reactors, pre-treatment strategies, the microbial culture used, and optimum operating condition have been presented. Through biological production, hydrogen production rates up to 52 L-H₂/L-medium/h and 6 L-H₂/L-medium/h for solid and liquid palm oil industrial waste, respectively, can be achieved. In short, the continuous supply of palm oil production by-product and relatively, the low cost of the biological method for hydrogen production indicates the potential source of renewable energy.

Agro-industrial wastewater in a circular economy: Characteristics, impacts and applications for bioenergy and biochemicals

The generation of agroindustrial byproducts is rising fast worldwide. The slaughter of animals, the production of bioethanol, and the processing of oil palm, cassava, and milk are industrial activities that, in 2019, generated huge amounts of wastewaters, around 2448, 1650, 256, 85, and 0.143 billion liters, respectively. Thus, it is urgent to reduce the environmental impact of these effluents through new integrated processes applying biorefinery and circular economy concepts to produce energy or new products. This review provides the characteristics of some of the most important agro-industrial wastes, including their physicochemical composition, worldwide average production, and possible environmental impacts. In addition, some alternatives for reusing these materials are addressed, focusing mainly on energy savings and the possibilities of generating value-added products. Finally, this review considers recent research and technological innovations and perspectives for the future.

Simulation and Optimisation of Integrated Anaerobic-Aerobic Bioreactor (IAAB) for the Treatment of Palm Oil Mill Effluent

This study highlights an innovative piece of hybrid technology, whereby the combination of anaerobic and aerobic processes into a single reactor, namely, the integrated anaerobic–aerobic bioreactor (IAAB) can surpass the limits of conventional methods treating palm oil mill effluent (POME). Optimisation of IAAB using SuperPro Designer V9 simulator for maximum biogas yield while addressing its economic and environmental trade-offs was conducted for the first time. Parameters such as hydraulic retention time (HRT) and organic loading rate (OLR) were optimised in the anaerobic compartment from 10 days and 6.2 g COD/L day to 9 days and 6.9 g COD/L day, respectively. Furthermore, sludge recycle ratio was optimised from 20% to 50% in the aerobic compartment. The optimisation was successful where the biogas yield increased from 0.24 to 0.29 L CH4/g CODremoved with excellent Chemical Oxygen Demand (COD), and Biological Oxygen Demand (BOD) removal efficiencies up to 99% with 5.8% lower net expenditure. This simulation results were comparable against the pre-commercialized IAAB with 11.4% increase in methane yield after optimisation. Economic analysis had proven the optimised process to be feasible, resulting in return on investment (ROI), payback time, and internal rate of return (IRR) of 24.5%, 4.1 years, and 17.9%, respectively.

Photocatalytic Technology for Palm Oil Mill Effluent (POME) Wastewater Treatment: Current Progress and Future Perspective

The palm oil industry produces liquid waste called POME (palm oil mill effluent). POME is stated as one of the wastes that are difficult to handle because of its large production and ineffective treatment. It will disturb the ecosystem with a high organic matter content if the waste is disposed directly into the environment. The authorities have established policies and regulations in the POME waste quality standard before being discharged into the environment. However, at this time, there are still many factories in Indonesia that have not been able to meet the standard of POME waste disposal with the existing treatment technology. Currently, the POME treatment system is still using a conventional system known as an open pond system. Although this process can reduce pollutants’ concentration, it will produce much sludge, requiring a large pond area and a long processing time. To overcome the inability of the conventional system to process POME is believed to be a challenge. Extensive effort is being invested in developing alternative technologies for the POME waste treatment to reduce POME waste safely. Several technologies have been studied, such as anaerobic processes, membrane technology, advanced oxidation processes (AOPs), membrane technology, adsorption, steam reforming, and coagulation. Among other things, an AOP, namely photocatalytic technology, has the potential to treat POME waste. This paper provides information on the feasibility of photocatalytic technology for treating POME waste. Although there are some challenges in this technology’s large-scale application, this paper proposes several strategies and directions to overcome these challenges.

Review on current approach for treatment of palm oil mill effluent: Integrated system

Malaysia is one of the countries that is well known for its palm oil based products and exports all over the world. Over the years, palm oil mill has been rising at alarming rate in Malaysia, causing palm oil-based wastes to increase especially palm oil mill effluent (POME). POME in Malaysia are channelled into water bodies such as rivers after treated mostly with conventional biological method. However, with current technologies and knowledge, conventional POME treatments are seen to be outdated and require major improvements as greenhouse gaseous are emitted to the environment as well as being less cost effective. Integrated systems that combine two or more conventional methods are introduced and reviewed to provide insights on the advantages and disadvantages of the system if it is to be implemented in real life plant. Integrated systems that focus on combining conventional methods are compiled and reviewed specifically for POME treatment. Among the integrated methods that are reviewed includes biological with membrane, adsorption with magnetic field exposure, adsorption with membrane and electrocoagulation with membrane. The systems are seen to give excellent color, chemical oxygen demand (COD) and total suspended solids (TSS) removal with average of higher than 90%. Reduction in space utilization, improved treatment time as well as simplified operating system were reported when integrated systems are applied as compared to conventional treatment of POME.

Microalgae Cultivation in Palm Oil Mill Effluent (POME) Treatment and Biofuel Production

Palm oil mill effluent (POME) is the wastewater produced during the palm oil sterilization process, which contains substantial amounts of nutrients and phosphorous that are harmful to the environment. High BOD and COD of POME are as high as 100,000 mg/L, which endanger the environment. Effective pre-treatment of POME is required before disposal. As microalgae have the ability of biosorption on nutrients and phosphorous to perform photosynthesis, they can be utilized as a sustainable POME treatment operation, which contributes to effective biofuel production. Microalgae species C. pyrenoidosa has shown to achieve 68% lipid production along with 71% nutrient reduction in POME. In this study, a brief discussion about the impacts of POME that will affect the environment is presented. Additionally, the potential of microalgae in treating POME is evaluated along with its benefits. Furthermore, the condition of microalgae growth in the POME is also assessed to study the suitable condition for microalgae to be cultivated in. Moreover, experimental studies on characteristics and performance of microalgae are being evaluated for their feasibility. One of the profitable applications of POME treatment using microalgae is biofuel production, which will be discussed in this review. However, with the advantages brought from cultivating microalgae in POME, there are also some concerns, as microalgae will cause pollution if they are not handled well, as discussed in the last section of this paper.

Enhanced volatile fatty acid production from sago hampas by Clostridium beijerinckii SR1 for bioelectricity generation using microbial fuel cells

Sago hampas is a starch-based biomass from sago processing industries consisted of 58% remaining starch. This study has demonstrated the bioconversion of sago hampas to volatile fatty acids (VFAs) by Clostridium beijerinckii SR1 via anaerobic digestion. Higher total VFAs were obtained from sago hampas (5.04 g/L and 0.287 g/g) as compared to commercial starch (5.94 g/L and 0.318 g/g). The physical factors have been investigated for the enhancement of VFAs production using one-factor-at-a-time (OFAT). The optimum condition; 3% substrate concentration, 3 g/L of yeast extract concentration and 2 g/L of ammonium nitrate enhanced the production of VFAs by 52.6%, resulted the total VFAs produced is 7.69 g/L with the VFAs yield of 0.451 g/g. VFAs hydrolysate produced successfully generated 273.4 mV of open voltage circuit and 61.5 mW/m² of power density in microbial fuel cells. It was suggested that sago hampas provide as an alternative carbon feedstock for bioelectricity generation.

Enzymatic pretreatment to enhance anaerobic bioconversion of high strength wastewater to biogas: A review

Oil and grease, carbohydrate, protein, and lignin are the main constituents of high strength wastewaters such as dairy wastewater, cheese whey wastewater, distillery wastewater, pulp and paper mill wastewater, and slaughterhouse wastewaters. These constituents have contributed to various operational problems faced by the high-rate anaerobic bioreactor (HRAB). During the hydrolysis stage of anaerobic digestion (AD), these constituents can be hydrolyzed. Since hydrolysis is known to be the rate-limiting step of AD, the overall AD can be enhanced by improving the hydrolysis stage. This can be done by introducing pretreatment that targets the degradation of these constituents. This review mainly focuses on the biological pretreatment on various high-strength wastewaters by using different types of enzymes namely lipase, amylase, protease, and ligninolytic enzymes which are responsible for catalyzing the degradation of oil and grease, carbohydrate, protein, and lignin respectively. This review provides a summary of enzymatic systems involved in enhancing the hydrolysis stage and consequently improve biogas production. The results show that the use of enzymes improves the biogas production in the range of 7 to 76%. Though these improvements are highly dependent on the operating conditions of pretreatment and the types of substrates. Therefore, the critical parameters that would affect the effectiveness of pretreatment are also discussed. This review paper will serve as a useful piece of information to those industries that face difficulties in treating their high-strength wastewaters for the appropriate process, equipment selection, and design of an anaerobic enzymatic system. However, more intensive studies on the optimum operating conditions of pretreatment in a larger-scale and synergistic effects between enzymes are necessary to make the enzymatic pretreatment economically feasible.

Co-digestion of palm oil mill effluent for enhanced biogas production in a solar assisted bioreactor: Supplementation with ammonium bicarbonate

Lack of sufficient nitrogenous substrate and buffering potential have been acknowledged as impediments to the treatment of palm oil mill effluent through co-digestion processes. In this study, ammonium bicarbonate was used to provide the nitrogenous substrate and buffering potential. To regulate the impact of ammonium bicarbonate toxicity on the anaerobic co-digestion system, dosages from 0 to 40 mg/L were supplemented. The biogas yield was used to indicate the effects of NH₄⁺ toxicity. In a solar-assisted bioreactor, solar radiation was first collected by a solar panel and converted into electricity, which was then used to heat a mixture of palm oil mill effluent and cattle manure to maintain the reactor in the mesophilic temperature range. This co-digestion operation was performed semi-continuously and was analyzed at a 50:50 mixing ratio of palm oil mill effluent and cattle manure. The results indicate that the additional dosing of ammonium bicarbonate can significantly enhance biogas production. Maximum cumulative biogas and methane productions of 2034.00 mL and 1430.51 mL, respectively, were obtained with the optimum addition of 10 mg/L ammonium bicarbonate; these values are 29.80% and 42.30% higher, respectively, than that obtained in the control co-digestion operation without addition of ammonium bicarbonate. Utilization of a mathematical equation (G = Gm^k/t) to describe a kinetic analysis of the biogas yield also indicated that the optimum ammonium bicarbonate dose was 10 mg/L. The results of this study suggest that supplementation with ammonium bicarbonate doses of up to 40 mg/L can be used to provide nitrogenous substrates and buffering potential in anaerobic co-digestion processes. The determination of the optimal dose provides an alternative and efficient option for enhanced biogas production, which will have obvious economic advantages for feasible industrial applications.

Integrated System Technology of POME Treatment for Biohydrogen and Biomethane Production in Malaysia

In recent years, production of biohydrogen and biomethane (or a mixture of these; biohythane) from organic wastes using two-stage bioreactor have been implemented by developing countries such as Germany, USA and the United Kingdom using the anaerobic digestion (AD) process. In Thailand, biohythane production in a two-stage process has been widely studied. However, in Malaysia, treating organic and agricultural wastes using an integrated system of dark fermentation (DF) coupled with anaerobic digestion (AD) is scarce. For instance, in most oil palm mills, palm oil mill effluent (POME) is treated using a conventional open-ponding system or closed-digester tank for biogas capture. This paper reviewed relevant literature studies on treating POME and other organic wastes using integrated bioreactor implementing DF and/or AD process for biohydrogen and/or biomethane production. Although the number of papers that have been published in this area is increasing, a further review is needed to reveal current technology used and its benefits, especially in Malaysia, since Malaysia is the second-largest oil palm producer in the world.

An evaluation of subcritical hydrothermal treatment of end-of-pipe palm oil mill effluent

This study evaluates the effects of subcritical hydrothermal treatment on palm oil mill effluent (POME) and its concomitant formations of solid hydrochar, liquid product and gaseous product. The reactions were carried out at temperatures ranged 493 K–533 K for 2 h. The highest reduction of chemical oxygen demand (COD) and biochemical oxygen demand (BOD) were 58.8% and 62.5%, respectively, at 533 K. In addition, the removal of total suspended solids (TSS) achieved up to 99%, with the pH of POME reaching 6 from the initial pH 4. The gas chromatography coupled with mass spectroscopy (GC-MS) analysis showed that the fresh POME contained n-Hexadecanoic acid as the dominant component, which gradually reduced in the liquid product in the reaction with increased temperature, in addition to the attenuation of carboxyl compounds and elevation of phenolic components. The gaseous products contained CO₂, CO, H₂, and C₃ – C₆ hydrocarbons. Traces of CH₄ were only found at 533 K. CO₂ is the dominant species, where the highest of 3.99 vol% per 500 mL working volume of POME recorded at 533 K. The solid hydrochars showed negligible morphological changes across the reaction temperature. The O/C atomic ratio of the hydrochar range from 0.157 to 0.379, while the H/C atomic ratio was in the range from 0.930 to 1.506. With the increase of treatment temperature, the higher heating value (HHV) of the hydrochar improved from 24.624 to 27.513 MJ kg^-1. The characteristics of hydrochar make it a fuel source with immense potential. POME decomposed into water-soluble compounds, followed by deoxygenation (dehydration and decarboxylation) in producing hydrochar with lower oxygen content and higher aromatic compounds in the liquid product. Little gaseous hydrocarbons were produced due to subcritical hydrothermal gasification at low temperature.

Feasibility analysis of homogenizer coupled solar photo Fenton process for waste activated sludge reduction

In this study, an attempt has been made to reduce the sludge using novel homogenizer coupled solar photo Fenton (HPF) process. At an optimum pH of 3 and Fe²⁺ to H₂O₂ dosage of 1:6, PF process yielded 63.7% solids reduction at a time interval of 45 min. Coupling of homogenizers with photo Fenton (PF) process effectively enhanced treatment efficiency. When homogenizer (specific energy - 1150.694 kJ/kg TS) was coupled with PF, a sharp increase in solid reduction 73.5% and decrease in reaction time (20 min) were observed. Cost benefit analysis revealed the efficiency of HPF process and achieved a net cost of 15.59 USD whereas PF achieved a negative net cost of -82.69 USD. Based on the above study it can be concluded that coupling of homogenizers with PF not only increased its efficiency but also make it field applicable.

Improvement of Methane Production from Sugar Beet Wastes Using TiO2 and Fe3O4 Nanoparticles and Chitosan Micropowder Additives

An experimental study was performed to measure biogas production from sugar beet waste, which is, in fact, the chopped parts of the sugar beet not going through the sugar extraction process, at different additive concentrations. Medium molecular weight chitosan in microsize and TiO₂ and Fe₃O₄ nanoparticles were added to ten experimental reactors to investigate their effect on the anaerobic digestion process. Three different concentrations of 0.01, 0.04, and 0.12% w/w were used for each additive. Biogas production and methane content were compared with a control sample containing no additive. Adding chitosan in powder form did not help the process nor improved methanogenic activities. The results showed no effect on anaerobic digestion by the addition of TiO₂ nanoparticles in the mentioned concentrations, whereas adding Fe₃O₄ nanoparticles led to a slight increase in methane production and in volatile solid and total solid reduction. The maximum enhancement in methane and biogas production in the sample containing 0.04% Fe₃O₄, as compared with the control sample, reached 19.77% and 15.09%, respectively.

Membrane-based zero-sludge palm oil mill plant

The palm oil industry is one of the most important agro-industries for tropical countries because of the unique properties and wide range of uses of palm oil for various end products. In a palm oil extraction process, a large quantity of water is required, of which half the quantity will end up as effluent. This palm oil mill effluent (POME) has an extremely high content of organic matter, which can cause severe pollution of waterways and other environmental problems. Disposal of this highly polluting effluent has become a major problem for the palm oil mills. Therefore, several methods have been proposed either to treat the POME so it could comply with environmental regulation while discharged or to recover water and other valuable components from the effluent. Membrane technology has emerged as a feasible alternative to conventional treatment in vegetable oil processing because of its attractive features such as low energy consumption, reduction in the number of processing steps, high separation efficiency, and improvement of the final product quality. In the case of POME treatment, an integrated membrane-based process promises efficient water recycling and total solid recovery from the effluent, thus eliminating the environmental problem. Recently, a novel concept combining oil–oil extraction and continuous filtration using a superhydrophobic membrane has been proposed to achieve a zero-sludge palm oil mill. In this concept, the huge wastewater effluent generated from the conventional process can be eliminated and the palm oil milling process simplified. Furthermore, the superhydrophobic membrane enables the production of high-purity palm oil. In this paper, we review the prospect of a zero-sludge palm oil mill concept and strategies to achieve the proposed concept. In addition, we also highlight the development of the superhydrophobic membrane and phytonutrient recovery.

Treatment of Palm Oil Mill Effluent Using Membrane Bioreactor: Novel Processes and Their Major Drawbacks

Over the years, different types of alternative technologies have been developed and used for palm oil mill effluent (POME) treatment. Specifically, membrane bioreactor (MBR) has been employed to relegate pollutants contained in POME under different operating conditions, and the technology was found to be promising. The major challenge impeding the wider application of this technology is membrane fouling, which usually attracts high operating energy and running cost. In this regard, novel methods of mitigating membrane fouling through the treatment processes have been developed. Therefore, this review article specifically focuses on the recent treatment processes of POME using MBR, with particular emphasis on innovative processes conditions such as aerobic, anaerobic, and hybrid processing as well as their performance in relation to fouling minimization. Furthermore, the effects of sonication and thermophilic and mesophilic conditions on membrane blockage were critically reviewed. The types of foulants and fouling mechanism as influenced by different operating conditions were also analyzed censoriously.

Microbiota of Palm Oil Mill Wastewater in Malaysia

This study was aimed at identifying indigenous microorganisms from palm oil mill effluent (POME) and to ascertain the microbial load. Isolation and identification of indigenous microorganisms was subjected to standard microbiological methods and sequencing of the 16S rRNA and 18S rRNA genes. Sequencing of the 16S rRNA and 18S rRNA genes for the microbial strains signifies that they were known as Micrococcus luteus 101PB, Stenotrophomonas maltophilia 102PB, Bacillus cereus 103PB, Providencia vermicola 104PB, Klebsiella pneumoniae 105PB, Bacillus subtilis 106PB, Aspergillus fumigatus 107PF, Aspergillus nomius 108PF, Aspergillus niger 109PF and Meyerozyma guilliermondii 110PF. Results revealed that the population of total heterotrophic bacteria (THB) ranged from 9.5 × 10⁵ - 7.9 × 10⁶ cfu/mL. The total heterotrophic fungi (THF) ranged from 2.1 × 10⁴ - 6.4 × 10⁴ cfu/mL. Total viable heterotrophic indigenous microbial population on CMC agar ranged from 8.2 × 10⁵ - 9.1 × 10⁶ cfu/mL and 1.4 × 10³ - 3.4 × 10³ cfu/mL for bacteria and fungi respectively. The microbial population of oil degrading bacteria (ODB) ranged from 6.4 × 10⁵ - 4.8 × 10⁶ cfu/mL and the oil degrading fungi (ODF) ranged from 2.8 × 10³ - 4.7 × 10⁴ cfu/mL. The findings revealed that microorganisms flourish well in POME. Therefore, this denotes that isolating native microorganisms from POME is imperative for effectual bioremediation, biotreatment and biodegradation of industrial wastewaters.

Treatment of palm oil mill effluent using combination system of microbial fuel cell and anaerobic membrane bioreactor

It was found that the operational temperature and the incorporation of microbial fuel cell (MFC) into anaerobic membrane bioreactor (AnMBR) have significant effect on AnMBRs' filtration performance. This paper addresses two issues (i) effect of temperature on AnMBR; and (ii) effect of MFC on AnMBRs' performance. The highest COD removal efficiency was observed in mesophilic condition (45°C). It was observed that the bioreactors operated at 45°C had the highest filtration resistance compared to others, albeit the excellent performance in removing the organic pollutant. Next, MFC was combined with AnMBR where the MFC acted as a pre-treatment unit prior to AnMBR and it was fed directly with palm oil mill effluent (POME). The supernatant from MFC was further treated by AnMBR. Noticeable improvement in filtration performance was observed in the combined system. Decrease in polysaccharide amount was observed in combined system which in turn suggested that the better filtration performance.

Life cycle assessment of superheated steam drying technology as a novel cow manure management method

Common methods of managing dairy manure are directly applying it to the farm field as a fertilizer. For direct application without any type of treatment, the majority of nutrients in the manure run off to the local river and lake during precipitation periods. The algae bloom is one of the environmental outcomes due to eutrophication of the lakes, which may jeopardize the quality of drinking water. In this study, superheated steam drying (SSD) technology is investigated as an alternative manure management method. Rapidly dried cow manure can be used as alternative fuel. Evaluations of energy payback time (EPBT) and life cycle assessment (LCA) of the SSD technology are presented in the SSD scenario and the results are compared with those of the direct field application (FA) of fresh manure and anaerobic digestion (AD). The heat required for the generation of superheated steam in the SSD scenario is provided from combustion of the dry manure to reduce energy costs. The results for the SSD process show 95% and 70% lower eutrophication and global warming potential in comparison to the FA scenario. Acidification potential for SSD turned out to be 35% higher than FA. The comparison of SSD with AD for their EPBT and normalized impacts indicated that the proposed SSD scenario has higher environmental sustainability than AD (70% lower impact), and is likely an economically better choice compared to conventional AD method (87% lower EPBT) for the future investment.

Palm oil mill effluent treatment and CO2 sequestration by using microalgae-sustainable strategies for environmental protection

In this era of globalization, various products and technologies are being developed by the industries. While resources and energy are utilized from processes, wastes are being excreted through water streams, air, and ground. Without realizing it, environmental pollutions increase as the country develops. Effective technology is desired to create green factories that are able to overcome these issues. Wastewater is classified as the water coming from domestic or industrial sources. Wastewater treatment includes physical, chemical, and biological treatment processes. Aerobic and anaerobic processes are utilized in biological treatment approach. However, the current biological approaches emit greenhouse gases (GHGs), methane, and carbon dioxide that contribute to global warming. Microalgae can be the alternative to treating wastewater as it is able to consume nutrients from wastewater loading and fix CO₂ as it undergoes photosynthesis. The utilization of microalgae in the system will directly reduce GHG emissions with low operating cost within a short period of time. The aim of this review is to discuss the uses of native microalgae species in palm oil mill effluent (POME) and flue gas remediation. In addition, the discussion on the optimal microalgae cultivation parameter selection is included as this is significant for effective microalgae-based treatment operations.

Trend and current practices of palm oil mill effluent polishing: Application of advanced oxidation processes and their future perspectives

Palm oil processing is a multi-stage operation which generates large amount of effluent. On average, palm oil mill effluent (POME) may contain up to 51, 000 mg/L COD, 25,000 mg/L BOD, 40,000 TS and 6000 mg/L oil and grease. Due to its potential to cause environmental pollution, palm oil mills are required to treat the effluent prior to discharge. Biological treatments using open ponding system are widely used for POME treatment. Although these processes are capable of reducing the pollutant concentrations, they require long hydraulic retention time and large space, with the effluent frequently failing to satisfy the discharge regulation. Due to more stringent environmental regulations, research interest has recently shifted to the development of polishing technologies for the biologically-treated POME. Various technologies such as advanced oxidation processes, membrane technology, adsorption and coagulation have been investigated. Among these, advanced oxidation processes have shown potentials as polishing technologies for POME. This paper offers an overview on the POME polishing technologies, with particularly emphasis on advanced oxidation processes and their prospects for large scale applications. Although there are some challenges in large scale applications of these technologies, this review offers some perspectives that could help in overcoming these challenges.

Phytoremediation of palm oil mill secondary effluent (POMSE) by Chrysopogon zizanioides (L.) using artificial neural networks

Artificial neural networks (ANNs) have been widely used to solve the problems because of their reliable, robust, and salient characteristics in capturing the nonlinear relationships between variables in complex systems. In this study, ANN was applied for modeling of Chemical Oxygen Demand (COD) and biodegradable organic matter (BOD) removal from palm oil mill secondary effluent (POMSE) by vetiver system. The independent variable, including POMSE concentration, vetiver slips density, and removal time, has been considered as input parameters to optimize the network, while the removal percentage of COD and BOD were selected as output. To determine the number of hidden layer nodes, the root mean squared error of testing set was minimized, and the topologies of the algorithms were compared by coefficient of determination and absolute average deviation. The comparison indicated that the quick propagation (QP) algorithm had minimum root mean squared error and absolute average deviation, and maximum coefficient of determination. The importance values of the variables was included vetiver slips density with 42.41%, time with 29.8%, and the POMSE concentration with 27.79%, which showed none of them, is negligible. Results show that the ANN has great potential ability in prediction of COD and BOD removal from POMSE with residual standard error (RSE) of less than 0.45%.

A modular diagnosis system based on fuzzy logic for UASB reactors treating sewage

A modular diagnosis system (MDS), based on the framework of fuzzy logic, is proposed for upflow anaerobic sludge blanket (UASB) reactors treating sewage. In module 1, turbidity and rainfall information are used to estimate the influent organic content. In module 2, a dynamic fuzzy model is used to estimate the current biogas production from on-line measured variables, such as daily average temperature and the previous biogas flow rate, as well as the organic load. Finally, in module 3, all the information above and the residual value between the measured and estimated biogas production are used to provide diagnostic information about the operation status of the plant. The MDS was validated through its application to two pilot UASB reactors and the results showed that the tool can provide useful diagnoses to avoid plant failures.

Outlining microbial community dynamics during temperature drop and subsequent recovery period in anaerobic co-digestion systems

To improve the stability of anaerobic reactors, more knowledge is required about how the different communities react against operating perturbations and which specific ones respond better. The objective of this work was to monitor the changes in microbial community structure of an anaerobic digester during a temperature drop by applying different complementary molecular techniques. Temperature decrease led to an increase of Bacteroidales order, Porphyromonadaceae family and Bacteroides genus and a decrease in Syntrophomonas and Clostridium genera. Once the temperature was restored, the reactor recovered the steady state performance without requiring any modification in operational conditions or in the microbiome. During the recovery period, Sedimentibacter genus and Porphyromonadaceae family played an important role in the degradation of the accumulated volatile fatty acids. The hydrogenotrophic methanogens appeared to be the keystone archaeal population at low temperatures as well as in the recovery period. This study stands out that the understanding of microbial community dynamics during temperature drop could be utilized to develop strategies for the mitigation of temperature change consequences and speed up the recovery of stable reactor performance.

Anaerobic Treatment of Palm Oil Mill Effluent in Pilot-Scale Anaerobic EGSB Reactor

Large volumes of untreated palm oil mill effluent (POME) pose threat to aquatic environment due to the presence of very high organic content. The present investigation involved two pilot-scale anaerobic expanded granular sludge bed (EGSB) reactors, continuously operated for 1 year to treat POME. Setting HRT at 9.8 d, the anaerobic EGSB reactors reduced COD from 71179 mg/L to 12341 mg/L and recycled half of sludge by a dissolved air flotation (DAF). The average effluent COD was 3587 mg/L with the consistent COD removal efficiency of 94.89%. Adding cationic polymer (PAM) dose of 30 mg/L to DAF unit and recycling its half of sludge caused granulation of anaerobic sludge. Bacilli and small coccid bacteria were the dominant microbial species of the reactor. The reactor produced 27.65 m(3) of biogas per m(3) of POME which was utilized for electricity generation.

Biomethane production and physicochemical characterization of anaerobically digested teff (Eragrostis tef) straw pretreated by sodium hydroxide

The biogas production potential and biomethane content of teff straw through pretreatment by NaOH was investigated. Different NaOH concentrations (1%, 2%, 4% and 6%) were used for each four solid loadings (50, 65, 80 and 95 g/L). The effects of NaOH as pretreatment factor on the biodegradability of teff straw, changes in main compositions and enhancement of anaerobic digestion were analyzed. The result showed that, using 4% NaOH for pretreatment in 80 g/L solid loading produced 40.0% higher total biogas production and 48.1% higher biomethane content than the untreated sample of teff straw. Investigation of changes in chemical compositions and physical microstructure indicated that there was 4.3-22.1% total lignocellulosic compositions removal after three days pretreatment with NaOH. The results further revealed that NaOH pretreatment changed the structural compositions and lignin network, and improved biogas production from teff straw.

Treatment of agro based industrial wastewater in sequencing batch reactor: performance evaluation and growth kinetics of aerobic biomass

A sequencing batch reactor (SBR) with a working volume of 8 L and an exchange ratio of 25% was used to enrich biomass for the treatment of the anaerobically treated low pH palm oil mill effluent (POME). The influent concentration was stepwise increased from 5000 ± 500 mg COD/L to 11,500 ± 500 mg COD/L. The performance of the reactor was monitored at different organic loading rates (OLRs). It was found that approximately 90% of the COD content of the POME wastewater was successfully removed regardless of the OLR applied to the SBR. Cycle studies of the SBR show that the oxygen uptake by the biomass while there is no COD reduction may be due to the oxidation of the storage product by the biomass. Further, the growth kinetic parameters of the biomass were determined in batch experiments using respirometer. The maximum specific growth rate (μmax) was estimated to be 1.143 day(-1) while the half saturation constant (Ks) with respect to COD was determined to be 0.429 g COD/L. The decay coefficient (bD) and biomass yield (Y) were found to be 0.131 day(-1) and 0.272 mg biomass/mg COD consumed, respectively.

Enhancement of Biodegradation of Palm Oil Mill Effluents by Local Isolated Microorganisms

This study was designed to investigate the microorganisms associated with palm oil mill effluent (POME) in Johor Bahru state, Malaysia. Biodegradation of palm oil mill effluents (POME) was conducted to measure the discarded POME based on physicochemical quality. The bacteria that were isolated are Micrococcus species, Bacillus species, Pseudomonas species, and Staphylococcus aureus, while the fungi that were isolated are Aspergillus niger, Aspergillus fumigatus, Candida species, Fusarium species, Mucor species, and Penicillium species. The autoclaved and unautoclaved raw POME samples were incubated for 7 days and the activities of the microorganisms were observed each 12 hours. The supernatants of the digested POME were investigated for the removal of chemical oxygen demand (COD), color (ADMI), and biochemical oxygen demand (BOD) at the end of each digestion cycle. The results showed that the unautoclaved raw POME sample degraded better than the inoculated POME sample and this suggests that the microorganisms that are indigenous in the POME are more effective than the introduced microorganisms. This result, however, indicates the prospect of isolating indigenous microorganisms in the POME for effective biodegradation of POME. Moreover, the effective treatment of POME yields useful products such as reduction of BOD, COD, and color.

Performance comparison between mesophilic and thermophilic anaerobic reactors for treatment of palm oil mill effluent

The anaerobic digestion of palm oil mill effluent (POME) was carried out under mesophilic (37°C) and thermophilic (55°C) conditions without long-time POME storage in order to compare the performance of each condition in the field of Sumatra Island, Indonesia. The anaerobic treatment system was composed of anaerobic hybrid reactor and anaerobic baffled filter. Raw POME was pretreated by screw decanter to reduce suspended solids and residual oil. The total COD removal rate of 90-95% was achieved in both conditions at the OLR of 15kg[COD]/m(3)/d. The COD removal in thermophilic conditions was slightly better, however the biogas production was much higher than that in the mesophilic one at high OLR. The organic contents in pretreated POME were highly biodegradable in mesophilic under the lower OLRs. The biogas production was 13.5-20.0l/d at the 15kg[COD]/m(3)/d OLR, and the average content of carbon dioxide was 5-35% in both conditions.

POME is treated for removal of color from biologically treated POME in fixed bed column: applying wavelet neural network (WNN)

As Malaysia is one of the world's largest producer of palm oil, large amounts of palm oil mill effluent (POME) is generated. It was found that negatively charged components are accountable for POME color. An attempt was made to remove residual contaminants after conventional treatment using anion base resin. Adsorption experiments were carried out in fixed bed column. Various models such as the Thomas, the Yoon-Nelson, the Wolborska and BDST model were used to fit the experimental data. It was found that only the BDST model was fitted well at the initial breakthrough time. A wavelet neural network model (WNN) was developed to model the breakthrough curves in fixed bed column for multicomponent system. The results showed that the WNN model described breakthrough curves better than the commonly used models. The effects of pH, flow rate and bed depth on column performance were investigated. It was found that the highest uptake capacity was obtained at pH 3. The exhaustion time appeared to increase with increase in bed length and decrease in flow rate.

Alternative technologies for the reduction of greenhouse gas emissions from palm oil mills in Thailand

Alternative methodologies for the reduction of greenhouse gas (GHG) emissions from crude palm oil (CPO) production by a wet extraction mill in Thailand were developed. The production of 1 t of CPO from mills with biogas capture (four mills) and without biogas capture (two mills) in 2010 produced GHG emissions of 935 kg carbon dioxide equivalent (CO2eq), on average. Wastewater treatment plants with and without biogas capture produced GHG emissions of 64 and 47% of total GHG emission, respectively. The rest of the emissions mostly originated from the acquisition of fresh fruit bunches. The establishment of a biogas recovery system must be the first step in the reduction of GHG emissions. It could reduce GHG emissions by 373 kgCO2eq/t of CPO. The main source of GHG emission of 163 kgCO2eq/t of CPO from the mills with biogas capture was the open pond used for cooling of wastewater before it enters the biogas recovery system. The reduction of GHG emissions could be accomplished by (i) using a wastewater-dispersed unit for cooling, (ii) using a covered pond, (iii) enhancing the performance of the biogas recovery system, and (iv) changing the stabilization pond to an aerated lagoon. By using options i-iv, reductions of GHG emissions of 216, 208, 92.2, and 87.6 kgCO2eq/t of CPO, respectively, can be achieved.