Palm oil is a popular ingredient in domestic products. The palm oil industry has been growing rapidly over the past decades, so that the amount of palm oil mill effluent (POME) generated from the palm oil production has been increasing as well. The anaerobic membrane bioreactor (AnMBR) is a treatment solution that can remove organic pollutants from POME while generating methane as an energy source. In comparison to conventional anaerobic digestors, the AnMBR technology has an additional membrane unit that can produce effluent with higher water quality. More specifically, if ultrafiltration is applied, the AnMBR will be able to effectively remove bacteria from the effluent, making it suitable for direct fertigation (Uman et al., 2021; Bray et al., 2021). However, in cases where infectious viruses are also present, further disinfection method might be required. In this experiment, a lab-scale AnMBR system was used for POME treatment. In order to evaluate how well the system can perform in terms of pollutant removal and methane production, under the controlled experimental conditions, several criteria were monitored: (1) chemical oxygen demand (COD) removal, (2) biomass growth, (3) biogas production, (4) digestion efficiency, and (5) volatile fatty acids (VFA) accumulation. A Long chain fatty acids (LCFA) analysis method was developed using the liquid chromatography/mass spectrometry (LC/MS), to elaborate on underlying conversion mechanisms. A COD balance analysis was also conducted. Factors that would potentially contribute to the COD gaps in the COD balance analysis were quantified and discussed in this paper as well to validate the experimental results. The solid retention time (SRT) was controlled at 140 days, and the organic loading rate (OLR) at 3 gCOD·L-1·d-1 during the first phase of the experiment, when synthetic POME and VFAs were added to the bioreactor. During the second phase, the SRT and the OLR of POME remained the same, whereas the VFAs were replaced by starch and the OLR of starch was increased, in order to simulate the real POME composition, because in addition to lipid, carbohydrate and protein are also found in POME. During Phase I, the AnMBR system could remove 98%-99% of the incoming COD, and produce about 5 L of methane each day. During Phase II, the microbes did not have enough time to adapt to the new experimental condition, but the stability of the AnMBR system could be achieved overtime, when the mixing is improved and the buffer solution is adjusted properly according to the pH variation. Although, based on the positive biomass net growth and the increased methane production, it could be predicted that adding carbohydrates to the feed for a more representative POME composition would promote biomass growth and methane production, suggesting that the AnMBR system would have higher potential when the real POME is used for energy recovery.

Palm oil mill effluent (POME) is a high organic pollution produced during the palm oil mill process, with a brownish color and stingy odor at high temperatures. Given the popularity in palm oil output over the years, the massive amount of POME causes growing concern. The enforcement of wastewater discharge standards and laws, as well as energy recycling of sustainability goals have facilitated the development of POME treatment processes. Several lab-scale studies have looked into the treatment of industrial wastewater using anaerobic membrane bioreactor (AnMBR) which has received considerable research interest due to its demonstrated potential for POME treatment. In this study, the synthetic POME was treated by a lab-scale crossflow anaerobic membrane bioreactor system. This study tested the feasibility of thermophilic PVDF-AnMBR systems for synthetic POME treatment, and meanwhile evaluated the biological and filtration performance of AnMBR treating lipid-rich wastewater at different sludge retention times (SRTs = 60 days, 90 days, and 140 days). AnMBR showed an adequate biological performance during the stabilizing state. The synthetic POME could be treated with over 98% of COD removal efficiency in all operational conditions. Plus, better digestion efficiency could be achieved at higher SRT (140 days). However, this study stresses that even though the membrane ensures biomass retention, the AnMBR process is still dodged by long-chain fatty acid (LCFA) accumulation and inhibition problems, especially at short SRT (60 days). The continuous reduction of biomass concentration during the stabilizing process of SRT at 60 days eventually resulted in the decreased methane production and system instability. Under all operational conditions, sufficient filtration performance and net permeate fluxes between 8 and 11 LMH were achieved. The trans-membrane pressure (TMP) was under 200 mbar throughout operating process. No membrane cleaning was needed. The results showed that better sludge filterability could be achieved at SRT of 90 days. The sludge filterability was compared as per the standard methods, including specific resistance to filtration and capillary suction time, which did not show a linear relationship with SRTs. Meanwhile, the physical-chemical characteristics of the sludge during the operational phases, including TSS concentrations and SMP, have a close correlation with sludge filterability parameters, such as capillary suction time and supernatant filterability.

Palm Oil Mill Effluent (POME) is an attractive medium for biogas production in an anaerobic membrane bioreactor (AnMBR) because of its high lipid content. Long-chain fatty acid (LCFA) accumulation is toxic and considered harmful for the biological performance within the reactor as they can be absorbed by biomass particles causing sludge flotation and biomass washout from the reactor. Membrane fouling can be caused by LCFA inhibition through adsorption on membrane walls. The biodegradation efficiency and filterability are affected by several factors such as solids retention time (SRT), and an organic loading rate (OLR). The objective of this research was to determine biological performance and LCFA inhibition while operating the AnMBR system at SRT of 90 days and an OLR of 3 g COD/ L/d under thermophilic condition (55 degrees Celcius).
It was observed that successful operation was achieved with high COD removal efficiencies over 98% and average biogas production of 5 NL/d. Acidification occur in the sludge causing signification drop in pH, biomass concentration and methane production. The reactor slowly recovered back normal after adding sodium bicarbonate in the VFA feed. In addition, acetic and propionic acid were the major VFA constituent presented in the sludge.

In palm oil extraction process, a large amount of lipids are emulsified in waste stream and the hot, brownish palm oil mill effluent (POME) is generated. In this study, the membrane technology was proposed to test the feasibility of direct ultrafiltration (UF) of POME by using a-Al2O3 and PVDF membranes, and to figure out the recovery rates of water and oi. POME synthesis methodology was successfully generated in the lab with the oil droplet size distribution and oil concentration conforming to the characteristics of real POME. The optimal operating conditions for POME filtration was determined by executing ultrafiltration experiments at different permeate fluxes and pHs. Both membrane shown good performance at original POME pH (pH 5). Compared with PVDF membrane, Al2O3 shown great strengths in higher optimal flux (57LMH), lower required trans-membrane pressure (TMP), higher oil and water recovery. The formation of oil layer on Al2O3 membrane reversed the charge type of membrane surface, which transformed oil droplet-membrane attraction to oil droplet-oil layer repulsion that allowed for the higher rejection and steady filtration process. The effect of SDS surfactant was also studied to clarify whether it could significantly improve membrane performance. The addition of SDS brought in extra pollutant with the SDS micelle size smaller than membrane pores, which reduced permeate quality and increased fouling in UF process. In the aspect of process stability, SDS benefited a-Al2O3 membrane performance more than PVDF membrane. The bi-layers SDS formed on a-Al2O3 membrane resulted in charge inversion and increased hydrophilicity of membrane surface that respectively enhanced anti-fouling property and membrane permeability. In the long run, SDS addition stabilized TMP variation process and prevented the sharp TMP increase. However, to guarantee the permeate quality of membrane technology, SDS was not recommended to be added. To operate POME process with more stable TMP and less fouling, a-Al2O3 membrane was highly recommended for POME treatment with great potential of industrial application in the future. The discussion of pH effect on membrane performance reveals other important affecting factors other than pH. Severe fouling of PVDF membrane happened below IEP_PVDF (pH 2). The increased hydrophobicity caused by oil layer formation could explain the lower membrane permeability and the adsorption of more hydrolyzed LCFA in acidic condition led to larger proportion of irreversible fouling. While the less excellent a-Al2O3 membrane performance at pH 10 was mainly due to the adsorption of more LCFA and glycerol onto membrane, despite the membrane-molecules/oil droplets repulsion existed in ultrafiltration. Although the general filtration mechanisms involves in almost all cases, the most important interactions that mainly function vary with different membrane and feed type.