Biogas Capture Research Articles

Greenhouse gas emissions along the value chain in palm oil producing systems: A case study of Cameroon

The agricultural sector is the second most emitting sector globally, contributing about 18% of total global greenhouse gas (GHG) emissions. Multipurpose high in-demand commodities like palm oil contribute significantly to these emissions. The Roundtable on Sustainable Palm Oil (RSPO) with an objective to make the palm oil sector sustainable, developed a new tool to quantify carbon emissions from palm oil mills. The PalmGHG tool has been used in Southeast Asia to measure carbon emissions from palm oil production and for palm oil certification. However, no studies have used the tool to evaluate GHG emissions from palm oil mills in sub-Saharan Africa, which contributes about 24% of global palm oil production and is home to one of the last remaining primary forests in the world. In this study, we quantify GHG emissions along the crude palm oil (CPO) life cycle in a growing palm oil producing region in Cameroon. We use the RSPO PalmGHG accounting tool, to identify sources of CO2 emissions and quantify them in tons of CO2 equivalent. Six mills across the South West and Center regions of Cameroon were sampled. We found that the sources of carbon emissions from our sampled mills in decreasing order of magnitude are land conversion (78%), palm oil mill effluent (21%), fertilizer use (0.9%), mill fuel combustion (0.1%) and grid electricity utilization (0.04%). The average GHG emissions per ton of crude palm oil produced were exceptionally high at 22.3 tCO2e compared to other palm oil producing regions in the world such as Indonesia with only 1.6 tCO2e/ton of CPO. In addition, we found that planting oil palm on previously logged land instead of primary forest conversion could prevent field emissions by up to about 89% and by up to about 69% for replanting old oil palm stands. Intensification measures like improving palm oil mill extraction rates and improving yields would drastically reduce emissions per ton of crude palm oil produced. Although land conversion associated with deforestation remains the major source of palm oil GHG emissions, farm and mill practices such as reduction in fertilizer use, biogas capture and use of clean energy could help reduce emissions in the long run.

Use of photo-driven algal-bacterial aerobic granular sludge system to close carbon cycle in biological nutrients removal and sludge anaerobic digestion units in wastewater treatment plants

This study established a closed photo-driven algal-bacterial aerobic granular sludge (AGS) system coupling with an automatic biogas capture unit and with a working volume of 800 mL operated at a gas circulation rate of 0.75 L/min and liquid pH controlled at 8.0. This closed system was used to investigate the feasibility of algal-bacterial AGS to capture and fix carbon (C) from nutrients removal and anaerobic digestion (AD) processes. Results showed a high total C emission of 0.93 kg-CO2/kg-chemical oxygen demand (COD) under the external O2 supply condition. However, under the photo-driven mode with photosynthesis as the sole O2 supplier, the coexisting microalgae fixed all inorganic C from the nutrients removal process with a negative C emission of −0.25 kg-CO2/kg-COD and −0.33 kg-CO2/kg-COD under illumination at 24 klux and 36 klux, respectively. During this process more HCl was required to neutralize the increased pH under a stronger light intensity, which can be replaced by biogas (as an acid reagent) automatically introduced into the closed system as needed. Meanwhile, a CO2 removal rate of 40 mg-C/(g-mixed liquor volatile suspended solids (MLVSS)•d) and a biogas upgrading rate of 184 mL-biogas/(g-MLVSS•d) were achieved under 24 klux. It was estimated that the CO2 removal capacity can cover all CO2 produced from AD of the grown biomass in this system. In addition, photosynthetic O2 could simultaneously facilitate aerobic phosphorus uptake and ammonia oxidation at a low dissolved oxygen of 0.7–1.4 mg/L. Results from this work suggest that a properly designed and operated algal-bacterial AGS is promising for closing C cycle in wastewater treatment plants.

Strategic Thinking for Bold Goals

Strategic Thinking for Bold Goals

Industry-driven mitigation measures can reduce GHG emissions of palm oil

Tropical peatland stores a large amount of carbon. In the last 20 years, drainage of Asian peat soil has increased to satisfy the demand of land for plantation agricultures. Industrial oil palm plantations occupy large areas of peatland in Indonesia and Malaysia, with associated GHG emissions and biodiversity loss, here referred to as nature occupation impact. This study performs a detailed Life Cycle Assessment (LCA) of 1 kg of palm oil for two case studies: PT SMART's Hanau and Sungai Rungau facilities in Central Kalimantan, Indonesia. The objective is to quantify the reduction in GHG emissions and nature occupation that has been achieved by implementing the following industry-driven measures: reducing the area of cultivated peat soil, reducing the peat drainage depth, and setting aside part of the land-bank for nature conservation. The results show that 1 kg of palm oil causes 2.72 and 2.25 kg CO 2 -eq./kg palm oil from Hanau and Sungai Rungau facilities respectively. These are 20%–34% lower than average RSPO certified palm oil and 49%–58% lower than average non-certified palm oil. Sungai Rungau achieves the reduction mainly due to a completely peat soil-free supply base. Hanau's peat emissions are instead 0.28 kg, compared to the 0.77 and 2.36 kg CO 2 -eq for RSPO certified and non-certified palm oil respectively, due to a very low drainage depth (18–25 cm compared to 57–73 cm in average of RSPO certified and non-certified respectively) and an overall lower share of oil palms on peat land. The impact on nature occupation is 24%–43% lower in Hanau and Sungai Rungau compared to non-certified oil and 4%–29% lower compared to RPSO certified respectively. About 8% of the total land bank of the Hanau supply-base has been set aside for nature conservation, reducing GHG emissions by 2% and nature occupation by 9%. Both Hanau and Sungai Rungau could also significantly reduce GHG emissions in the palm oil milling stage, by implementing biogas capture in palm oil mill effluent (POME) treatment. • Avoiding the cultivation of peat soil reduces the GHG emissions of palm oil production. • When oil palms are on peat soil, reducing the peat drainage depth reduces the GHG emissions. • Nature conservation initiatives reduce GHG emissions and nature occupation of palm oil production. • Capturing the biogas produced in palm oil mill effluents (POME) treatment reduces GHG emissions. • Using the captured biogas in boiler or biogas engine further abates the GHG emissions of palm oil.

A critical analysis on biogas production and utilisation potential from palm oil mill effluent

The conventional method used for palm oil mill effluent (POME) treatment is associated with several environmental issues that affect the sustainable production of palm oil. Integrated POME treatment with a closed anaerobic digester is identified as a practical cleaner production approach to mitigate global issues on energy security and climate change and enhance the sustainability of the industry. This paper discusses the potential of capturing biogas to the palm oil industry and Malaysia's renewable energy (RE) and greenhouse gases (GHG) emissions targets. Approximately 75% GHG reduction could be achieved for every t of crude palm oil produced from palm oil mill with biogas capture. In total, 1750 million m3 biogas with GHG savings of 19.5 million t CO2eq can be achieved annually, if all palm oil mills in Malaysia capture the biogas. A 540 MW installed capacity or 37 million MMBtu in the form of bio-compressed natural gas (Bio-CNG) or biomethane, can supplement the nation's energy mix for the sustainable energy generation. These contribute towards enhancing the sustainability criteria and economic performance of the palm oil mills by adopting cleaner production technology of POME treatment for circular economy and better market access of palm oil products. Future work should emphasise on nationwide biogas implementation through synergising and strengthening private commitments and the government supports.

Formation mechanisms and mechanical properties of anaerobic lagoon scum

The formation of a floating scum layer on the liquid surface of covered anaerobic lagoons prevents optimal and efficient lagoon operation. Scum can reduce hydraulic retention time, inhibit biogas capture and cause damage to lagoon covers. Managing the negative impact of scum requires understanding what scum is, how it forms and how it consolidates.This paper presents measurements of the physical and mechanical properties of scum and sludge samples from two covered anaerobic lagoons that alternatively treat municipal and abattoir waste. Both scum samples consisted of a large proportion of suspended solids that sank once the sample was diluted, degassed and mixed, indicating that sludge flotation and buoyancy due to biogas generation is a major contributor to scum accumulation. Total and soluble chemical oxygen demand and volatile solids in the scum are approximately 90 % higher than in sludge, which indicates that scum has a large proportion of undigested solids. Fourier-transform infrared spectroscopy demonstrates that scum and sludge have similar organic matter, with both including fats, oils, greases, proteins, and polysaccharides.Scum formation due to gas buoyancy implies that scum accumulation is inevitable and controlling fats, oils, and greases at the source of the wastewater is not enough to stop scum formation. Scum accumulation increases due to buoyancy, which drives scum compaction and increases the strength of the scum, as demonstrated by the measurement of scum compressional rheology. Scum management techniques that disturb the scum layer early enough to release the entrapped gas enable the scum to sink and get digested, thus minimising the impact of scum formation.

Life‐cycle greenhouse gas emissions in power generation using palm kernel shell

AbstractPalm kernel shell (PKS) utilization for power generation has greatly increased in Japan since the introduction of the feed‐in tariff (FIT) in 2012. However, the FIT fails to consider the entire palm industry while evaluating the environmental impacts of using PKS. Therefore, this study aimed to elucidate the life‐cycle greenhouse gas (GHG) emissions of power generation using PKS. We targeted two PKS‐firing power plants as these are the first two instances of the use of PKS in power plants in Japan. A system boundary was established to cover palm plantation management in Indonesia and Malaysia, as both power plants import PKS from these countries. The GHG emissions were derived from land‐use change, palm plantation, oil extraction, PKS transportation, and power plants. Six scenarios were examined for the emissions based on the type of land‐use change and the existence of biogas capture in oil extraction. CO2 emissions from PKS combustion were also calculated by assuming that carbon neutrality was lost because of cultivation abandonment. The GHG emissions in one scenario, where the plantations were replanted and continuously managed and no biogas capture implemented in oil extraction, exhibited an average of 0.134 kg‐CO2eq/kWh reduction in a plant in Kyushu District, and 0.043 kg‐CO2eq/kWh reduction in a plant in Shikoku District for liquid natural gas‐fired steam power generation, respectively. More than 65% of life‐cycle GHG emissions originate from biogas generated during oil extraction; thus, biogas capture is an effective strategy to reduce current emissions. In contrast, in the case of accompanying land‐use change or collapse of carbon neutrality, the emissions considerably exceeded those of fossil fuels. These findings indicated that the FIT fails to consider the risk of increased emissions or further substantial emission reductions. Therefore, the feasibility of FIT application to PKS needs to be re‐established by evaluating the entire PKS life cycle.

GHG analysis of the production of crude palm oil considering the conversion of agricultural wastes to by-products

The oils and fats world production are predominantly championed by two (2) main oils which are palm oil and soybean oil. Even though these commodities are categorized as oils, these crops are basically agricultural crops which generate abundant wastes along their supply chain. The oil palm supply chain churns out huge amounts of biomass and water wastes. Greenhouse gas (GHG) analysis was conducted for four (4) different pathways practiced by the Malaysian oil palm industry which analyses the GHG emissions of these pathways and also included the recycling of the wastes. The GHG emissions from for land use change (LUC) from logged over forest, oil palm fresh fruit bunch production and biogas were 2095, 618, 916 kg CO 2 eq/kg CPO respectively. The recycling of pressed mesocarp fiber (PMF) and palm kernel shell (PKS) as fuel displaced 2.5 kWh/kg PMF and 3.6 kWh/kg PKS of fossil energy giving a GHG reduction of 1.5 kg CO 2 eq /kg PMF and 2.2 kg CO 2 eq/kg PKS, respectively. The empty fruit bunch (EFB) applied at the plantations for mulching as fertilizer substitute gave a GHG savings of 3.3 kg CO 2 eq/t EFB. EFB used as boiler fuel displaced 2.0 kWh/ kg EFB of electricity with a GHG savings of 1.1 kg CO 2 eq /t EFB. Palm oil mill effluent (POME), wastewater of the milling process emits biogas during the anaerobic treatment, when captured and utilized as energy, displaces 2.7 kWh/m 3 biogas of non-renewable energy with GHG savings of 13.4 kg CO 2 eq/m 3 biogas. Pathway one (1) with LUC from logged over forest, biogas emissions and biomass utilization as fuels and fertilizer substitute showed the worst environmental performance while pathway 4 with no LUC, biogas capture and utilization of biomass as fuels showed the best environmental performance to produce crude palm oil.

Biogas production enhancement by co-digestion of empty fruit bunch (EFB) with palm oil mill effluent (POME): Performance and kinetic evaluation

The palm oil industry is gearing itself towards sustainability by implementing mandatory biogas capture for all palm oil mills in the effort to reduce greenhouse gases. This action also indicates that the anaerobic digestion of palm oil mill effluent (POME) will be one of the essential sources of biogas for energy generation. However, the availability of POME is limited during the low crop season due to the lower palm oil production. Concurrently, the solid wastes known as empty fruit bunches (EFB) are also produced from the oil mill. EFB has vast potential for power generation, though it is currently not being fully utilized. Therefore, this work aims to enhance the biogas production from anaerobic co-digestion (ACD) of EFB with POME by evaluating the effect of alkaline pretreatment of EFB, EFB-to-POME ratio, and temperature on the methane yield. The optimum EFB:POME ratio is 0.6:1 as the methane production of this ratio at both thermophilic and mesophilic conditions are relatively high (up to 74.02 ml CH4/g VS). Results show that ACD performs 2.36 times better than mono-digestion of POME at mesophilic conditions. The modified Gompertz model could predict the process behavior of the ACD of EFB with POME with high R2 (>0.95). Further investigation on other potential pretreatment methods and synergism analysis of co-digestion, which provides a balance between efficiency and economy could be carried out. The impact of this work will be towards a sustainable environment, which will significantly reduce the environmental impacts of palm oil production.

Transformation of Waste Stabilization Ponds: Reengineering of an Obsolete Sewage Treatment System

Waste Stabilization Ponds (WSPs) are commonly used for sewage treatment. These systems are composed of a series of ponds: (1) anaerobic ponds, (2) facultative ponds, and (3) maturation ponds. WSPs generally produce good-quality effluent in terms of organic matter and pathogen removal, but their application has disadvantages. The most serious disadvantages are a long retention time, the release of biogas, and the impossibility of removing nutrients. A promising alternative to the use of WSPs is replacing the anaerobic pond and facultative pond with an upflow anaerobic sludge blanket (UASB) reactor, with the advantages of greatly reducing the retention time and the biogas capture. The post-treatment ponds of the UASB reactor effluent involve oxygen production and the biological consumption of carbon dioxide, which raises the pH. An experimental investigation showed that it is possible to use polishing ponds in a sequential batch regime instead of continuous flow. This modification accelerates the decay of pathogens and accelerates the increase in pH, which, in turn, facilitates the removal of nitrogen and phosphorus. This produces a good-quality effluent with low concentrations of biodegradable organic material, nutrients, and pathogens. This good-quality effluent is obtained in a system without energy consumption or auxiliary materials and with a much smaller area than conventional stabilization ponds.

A brief review on biochemical oxygen demand (BOD) treatment methods for palm oil mill effluents (POME)

Numerous issues pertaining to palm oil mill effluents (POME), such as the release of high level of biochemical oxygen demand (BOD) and other pollutants into the environment, have brought major public concern. Hence, Department of Environment (DOE) has implemented stricter laws on the final discharge of POME, whereby BOD must be less than 20 mg L −1 . Addressing that, the recent types of treatment methods to reduce BOD were briefly reviewed in this article. A lower value of BOD can be achieved by improving both biological and physiochemical treatment methods for POME. The palm oil industry has also recently combined the existing treatment and biogas capture technology to create an integrated system to reduce BOD effectively, and at the same time, make full use of the valuable by-products, such as methane gas, as part of the effort to realise the idea of zero discharge waste. In conclusion, based on the previous studies, of whether in small or large scale, it is recommended to include information of BOD reduction for future research guidelines, which can be used to address related palm oil waste discharge issues for better environmental quality. • Various BOD treatment methods for POME has been reviewed. • The research gap due to the new 20 mg/L BOD discharge limit is mentioned. • Sonochemical oxidation with activated carbon adsorbent removed 100% of BOD. • Integrated system technology is found to be the best solution for BOD treatment.

Certified palm oil reduces greenhouse gas emissions compared to non-certified

Consumers are increasingly demanding products containing palm oil produced without harm to the environment. The industry response to this demand has been the creation of the Roundtable on Sustainable Palm Oil (RSPO) and the development of a certification system to ensure sustainable palm oil production. However, currently there is no scientific evidence of the benefit gained through the RSPO certification schema. This paper quantifies the environmental impacts of RSPO certified and non-certified through a detailed Life Cycle Assessment (LCA) of 1 kg of RBD palm oil to factory gate, produced in Indonesia and Malaysia in 2016, to identify potential benefits and trade-offs of RSPO certification. The ISO 14040/14044 compliant LCA is carried out following both a consequential and an attributional LCA approach. The inventory model presents a high level of detail. Primary inventory data describing the certified production system are obtained from RSPO assessment reports, covering 73% (634 estates) of the certified estate, including 111 smallholders, and 58% (165 oil mills) of the certified mills. Data for the total industrial production are drawn from national statistics and scientific literature. The non-certified flows are derived by subtracting the certified flows from the total industry flows. The consequential results show that RSPO certified oil reduces GHG emission by 35% compared to non-certified i.e. 3.41 (2.61–4.48) kg CO2 eq./kg for certified vs 5.34 (3.34–8.16) kg CO2 eq./kg for non-certified. Based on a thorough data quality assessment and uncertainty analysis, this result is deemed sufficiently robust and thus conclusive. Certified production achieves the largest GHG emissions reduction because of higher yields, i.e. less land use per unit of product, less oil palm cultivated on peat soil and higher share of palm oil mill effluents treated with biogas capture technologies. We also found that nature occupation is reduced by 20% in certified production while respiratory inorganic is slightly higher (3%) in certified production, due to the larger use of fertilisers. For other impact categories, results are associated with a larger uncertainty and therefore shall be considered as indicative. Similar results are found in attributional modelling.

Simulation and optimisation of full-scale palm oil mill effluent (POME) treatment plant with biogas production

Palm oil mill effluent (POME) is the primary source of water pollution in the oil palm industry. Most palm oil mills are employing a series of anaerobic and aerobic ponds for POME treatment, in order to comply with environmental regulation. In recent years, some mills are installed with biogas capture facilities in order to reduce the emission of greenhouse gas, as well as to raise some profits. In this work, a covered lagoon process for POME treatment, coupled with biogas production was modelled using commercial process simulation software SuperPro Designer v9.0. The simulation results revealed that 29 m3 of biogas can be produced per tonne of treated POME, with a removal efficiency of 92 % for its chemical oxygen demand (COD). Cost analysis has proven that the process is economically viable, with a net present values of $ 2,830,000, IRR of 14.3 %, and payback time of 4.66 years. Process optimisation revealed that the optimal recycle ratio of sludge should be set to 30 %, where the minimum net expenditure ($11,812/y) is achieved, with final effluent COD content of 18 ppm. Note that this takes into consideration of the trade-off between capital and operating costs.

Assessing water footprint for the oil palm supply chain- a cradle to gate study

Water footprint (WFP) has gained importance due to the increase of water scarcity in the world. This paper analyses the WFP the oil palm supply chain (cradle to gate) which produces oil palm fresh fruit bunch (FFB), crude palm oil, palm kernel and crude palm kernel oil. The water accounting and vulnerability evaluation (WAVE) method was used. This method analyses the water depletion index (WDI) based on the local blue water scarcity. The main contribution towards the WFP at the plantation was the production of FFB from the crop. At the mill the burden shifts to the water added during the process which consists of the boiler and process water. There was a 33 % reduction in the WFP when there was no dilution or water addition after the screw press at the mill. When weight allocation was performed the WFP reduced by 42 % as the burden was shared with the palm kernel and palm kernel shell. At the kernel crushing plant (KCP), the main contributor towards the WFP came from the palm kernel which carried the burden from upstream followed by electricity used for the process and transportation of the palm kernel. Two sensitivity analysis was carried out, first for mills with biogas capture versus no biogas capture and the WFP had no difference for both scenarios. Second was comparison between weight, economic and energy allocation Weight and economic allocation gave a 42% and 38% reduction respectively while energy allocation gave a 60% reduction to crude palm oil. The comparison when the KCPs operate in the proximity of mills as compared to those operating in the proximity of ports only gave a reduction of 6 % for the WFP. The milling stage had the most significant impact on the WFP. Mills should avoid dilution to reduce this impact.

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.

Optimal Design of Integrated Palm Oil Complex with Palm Oil Mill Effluent Elimination Strategy

Palm oil mill effluent (POME) is one of the biggest pollution sources due to its eutrophying nature and methane emitting treatment technology. Although biogas capture and utilisation have been widely encouraged to achieve greenhouse gas (GHG) mitigation in palm oil mills (POM), most Malaysian POMs still find it economically infeasible to invest in proper biogas facilities. Hence, POME elimination should be considered as one of the waste management options in synthesising palm oil processing pathway for profit enhancement and GHG mitigation. One of the solutions to achieve sustainability in palm oil industry is to integrate POM and palm oil refinery (POR) in terms of waste management, energy and resource. Therefore, it is desired to design an optimally integrated palm oil based-complex (POBC) which considers POME evaporation approach. The main objective of this study is to develop a model to aid POBC planning via synthesis of an integrated resource and utility network considering POME elimination with maximum profit. Based on the case study, maximum USD 36.65 x 106 is obtained for the optimal POBC design with POME elimination pathway selected. The optimum production rate for Refined, Bleached, Deodorised Palm Olein (RBDPOL) is 10.309 t/h which is boosted compared to the baseline study. 61 % less water demand is also achieved. The research output, the developed model and optimal network shall provide input to POM owners on optimal POME management and determine the economic feasibility of proposed POBC in Malaysia.

SUSTAINABLE BIOMETHANE: METHANE SLIP REMOVAL APPLYING REGENERATIVE CATALYTIC OXIDATION (RCO) POST COMBUSTION TECHNOLOGY

Biomethane is incentivized in Italy and in many other European countries as a substitute fuel for transport, in order to reduce fossil fuel and cut CO2 emissions. In Italy, Certificato di Immissione in Consumo (CIC) is actually sustaining biomethane production, charging petrochemical companies who need to cover their obligation quotes. Actually, biomethane production has to fulfil sustainability requirements in order to be entitled to get CIC. Sustainability principles are, among others, the type of feeding, total biogas capture during the fermentation process and last but not least, a very low methane loss associated to the off-gas of the upgrading unit, actually set at < 1 % CH4 in Italy and most probably further reduced in the short. The upgrading unit off-gas, therefore, has to respect the limit, or as an alternative, it has to be treated in a post-combustion unit. There are technical upgrading solutions on the market that can achieve methane loss < 1% CH4, but incremental energy, operating and investment cost have to be considered in a cost-benefit evaluation. Post-combustion on the other hand can be a serious issue, since the flow to be burnt does not contain oxygen at all, just traces of methane (normally 2-3%) and CO2 (97-98%), changing dramatically operating conditions of traditional post-combustor units applied to cogeneration engines off-gas. For the biomethane off-gas combustion, a sustainable cost-effective solution is the Regenerative Catalytic Oxidation (RCO), operating at lower temperature than Thermal Oxidation (TO), therefore reducing energy costs and improving environmental footprint. The purpose of this article is to compare the Regenerative Thermal Oxidizer (RTO) with the Regenerative Catalytic Oxidizer (RCO).

High-rate anaerobic treatment of digestate using fixed film reactors

The effluent stream of the anaerobic digestion processes, the digestate, accommodates high residual organic content that needs to be further treated before discharge. Anaerobic treatment of digestate would not only reduce the residual organic compounds in digestate but also has a potential to capture the associated biogas. High-rate anaerobic reactor configurations can treat the waste streams using lower hydraulic retention times which requires less footprint opposed to the conventional completely stirred tank reactors. This study investigated the high-rate anaerobic treatment performance and the associated biogas capture from the digestate of a manure mixture composed of 90% laying hen and 10% cattle manures in fixed-film reactors. The results indicated that it was possible to reduce total chemical oxygen demand content of the digestate by 57–62% in 1.3–1.4 days of hydraulic retention time. The corresponding biogas yields obtained were in the range of 0.395–0.430 Lbiogas/g VSadded which were found to be comparable to many raw feedstocks. Moreover, significant total phosphorus reduction (36–47%) and greenhouse gas capture (over 14.5–18.1 tCO2e/d per m3 digestate) were also recorded in the anaerobic fixed-film reactors.

Anaerobic treatability and residual biogas potential of the effluent stream of anaerobic digestion processes.

Although anaerobic digestion is a well-established technology, the treatment and disposal of the digestate still presents a challenge due to lack of viable methods for processing. The residual organic matter in digestates also creates a significant residual biogas potential. This fact indicates that the digestates need further processing not only to reduce their organic content for disposal, but also to capture the biogas associated with this residual organic content. This study investigated anaerobic treatment and residual biogas potential of digestates obtained from five full-scale farm-based digesters. The results indicated that it was possible to reduce the total chemical oxygen demand (CODt ) of the digestates with an efficiency of 21%-84%. The corresponding biogas yields of digestates ranged between 0.078 and 0.326Lbiogas /g VSadded . This level of biogas production is comparable to the biogas production potential of several commonly used raw substrates. PRACTITIONER POINTS: Significant CODt reduction and biogas capture can be attained by AD of digestates. The digestates subjected to anaerobic treatment yielded up to 82% CODt removal. Residual biogas yields of digestates ranged between 0.078-0.326 Lbiogas/g VSadded. Biogas yields obtained were comparable to many raw feedstocks of biogas plants.

Charting the water footprint for Malaysian crude palm oil

Abstract Water scarcity is a serious issue facing our planet right along -side with climate change. The purpose of this study was to evaluate the impacts associated with the use of water by the oil palm trees and the industry for the production of crude palm oil in Malaysia; evaluate the uncertainties of the outcome of a study based on pathway assumptions and the choice of allocation. A full life cycle assessment and a stand-alone water footprint value based on the local water stress index has been determined. The system boundary included the oil palm nursery, plantation (with land use change of oil palm to oil palm and from logged over forest) and palm oil mill (biogas capture scenario). The results showed that the direct water used by the crops and process was minimal because the oil palm plantations in Malaysia were firstly rain fed and not irrigated and secondly Malaysia is located in a region with high availability of renewable water resulting to a low water stress index. The water footprint concluded that the main potential impacts within the system boundary were dominated by land conversion, production and use of fertilisers and pesticides. These findings contradict the general perception of any agriculture system where the notion to assume that the water used by the crop will have the major potential impact. The findings also highlighted the importance of the choice of pathway, government initiatives and managerial intervention for biogas capture which resulted to a 117% reduction in the water footprint. Economic allocation had a 21% increase in the water footprint as compared to weight allocation. It was recommended that plantations implement Good Agricultural Practices that addresses the key elements of land, water management, fertiliser and integrated pest management and the choice of pathways and allocation procedures are made transparent with the results as outcomes may differ as shown in this paper.