Enhancing digestion efficiency of POME in anaerobic sequencing batch reactor with ozonation pretreatment and cycle time reduction

A review on the pollution assessment of hazardous materials and the resultant biorefinery products in Palm oil mill effluent

The voluminous nature of palm oil mill effluent (POME) is directly associated with environmental hazards and could be turned into biorefinery products. The POME, rich in BOD, COD, and oil and grease, with few hazardous materials such as siloxanes, fatty acid methyl ester, and phenolic compounds that may significantly increase the risk of violating the effluent quality standards. Recently, the application of chemical and biological risk assessment that can use electrochemical sensors and microalgae-like species has gained paramount attention towards its remediation. This review describes the existing risk assessment for POME and recommends a novel assessment approach using fish species including invasive ones as suitable for identifying the toxicants. Various physico-chemical and biological treatments such as adsorption, coagulation-flocculation, photo-oxidation, solar-assisted extraction, anaerobic digestion, integrated anaerobic-aerobic, and microalgae cultivation has been investigated. This paper offers an overview of anaerobic technologies, with particular emphasis on advanced bioreactors and their prospects for industrial-level applications. To illustrate, palmitic acid and oleic acid, the precursors of fatty acid methyl ester found in POME pave the way to produce biodiesel with 91.45%. Although there are some challenges in attaining production at an economic scale, this review offers some opportunities that could help in overcoming these challenges.

Holistic process evaluation of non-conventional palm oil mill effluent (POME) treatment technologies: A conceptual and comparative review

Thriving oil palm agroindustry comes at a price of voluminous waste generation, with palm oil mill effluent (POME) as the most cumbersome waste due to its liquid state, high strength, and great discharge volume. In view of incompetent conventional ponding treatment, a voluminous number of publications on non-conventional POME treatments is filed in the Scopus database, mainly working on alternative or polishing POME treatments. In dearth of such comprehensive review, all the non-conventional POME treatments are rigorously reviewed in a conceptual and comparative manner. Herein, non-conventional POME treatments are sorted into the five major routes, viz. biological (bioconversions - aerobic/anaerobic biodegradation), physical (flotation & membrane filtration), chemical (Fenton oxidation), physicochemical (photooxidation, steam reforming, coagulation-flocculation, adsorption, & ultrasonication), and bioelectrochemical (microbial fuel cell) pathways. For aforementioned treatments, the constraints, pros, and cons are qualitatively and quantitatively (with compiled performance data) detailed to indicate their process maturity. Authors recommended (i) bioconversions, adsorption, and steam reforming as primary treatments, (ii) flotation and ultrasonication as pretreatments, (iii) Fenton oxidation, photooxidation, and membrane filtration as polishing treatments, and (iv) microbial fuel cell and coagulation-flocculation as pretreatment or polishing treatment. Life cycle assessments are required to evaluate the environmental, economic, and energy aspects of each process.

Modeling ozonation pretreatment parameters of distillery wastewater for improved biodegradability

In this study, ozonation pretreatment of real distillery wastewater (DWW) for biodegradability enhancement was undertaken. Response surface methodology was used to model the value of effective parameters, including ozonation duration and initial chemical oxygen demand (COD) concentration, and to estimate linear interactions and quadratic effects. The analysis of variance confirmed the adequate description of all the responses by the quadratic model employed. During ozonation, the pH of the DWW increased in acidity from 4.53 to 4.05, indicating the formation of acidic intermediates. A 60% reduction in color was observed signifying the oxidation of the color causing biorecalcitrant aromatic compounds and confirmed by the reduction in ultraviolet absorbance at λ_max of 254 nm. Moreover, an increase in change in oxidation state from -0.1 to 0.4 was attributed to the declined aromaticity and the formation of aliphatic structures. From the measurement of the ratio of biochemical: chemical oxygen demand (BOD₅:COD), an increase from 0.48 to 0.72 confirmed improved biodegradability. Optimization studies aimed at achieving maximum improved biodegradability at maximum ozone transfer efficiency yielded optimum ozonation pretreatment parameters of initial COD of 4.1 g L^-1 and duration of 64 min.

Photocatalytic degradation of P-Cresol using TiO2/ZnO hybrid surface capped with polyaniline

This study evaluated the photocatalytic activity of polyaniline (PANI)-capped titanium dioxide and zinc oxide (TiO₂/ZnO) hybrid, for the degradation of P-Cresol. The hybrid was synthesized by precipitating ZnO on the surface of commercial TiO₂. An "in situ" chemical oxidative polymerization method was used to prepare the PANI capped hybrid (TiO₂/ZnO/PANI). The photocatalysts were characterized by powder X-ray diffraction (XRD), a Brunauer Emmett Teller (BET) analyzer, Fourier-transform infrared (FTIR) and photoluminescence spectroscopies, high resolution-transmission electron microscopy (HR-TEM) and thermogravimetric analysis (TGA). During photodegradation under ultraviolet (UV) irradiation, ZnO, TiO₂, TiO₂/ZnO hybrid and TiO₂/ZnO/PANI composite had P-Cresol removal of 43%, 50%, 61% and 99%, respectively. The higher activity of the TiO₂/ZnO hybrid as compared to TiO₂ and ZnO was attributed to a reduced electron-hole pair recombination. The recombination was further significantly reduced upon introduction of PANI; hence, the highest activity observed with TiO₂/ZnO/PANI. The initial reaction rate constant for TiO₂/ZnO/PANI (0.9679 min^-1) was more than twice compared to that for TiO₂/ZnO hybrid (0.1259 min^-1). A synergistic effect between PANI and TiO₂/ZnO resulted in a highly efficient charge separation caused by the transfer of photogenerated holes from the hybrid to highest occupied molecular orbitals (HOMO) of PANI. The best TiO₂/ZnO/PANI (PANI to TiO₂/ZnO) ratio observed was 0.5:2 for the photodegradation of P-Cresol. Total organic carbon (TOC) analysis indicated a 97.4% mineralization of P-Cresol with PANI/TiO₂/ZnO.

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.

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.

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.

Sonolysis and ozonation as pretreatment for anaerobic digestion of solid organic waste

This study aims to compare the efficiency of sonolysis and ozonation in improving anaerobic biodegradability of source sorted organic fraction of municipal solid waste, for the enhancing of biogas production and energy recovery as well. The methane yield of solid organic material anaerobic digestion is significantly affected by substrate availability, which can be favoured by pretreatments. In this investigation, both sonolysis and ozonation effects on substrate solubilisation and anaerobic biodegradability were evaluated under different treatment conditions. Results show that both pretreatments can significantly improve the solubilisation of organic solid waste. However, during ozonation experiments, no correlation was observed between increased solubilisation and biogas production: the application of higher ozone doses led to the formation of by-products less biodegradable than untreated substrate. This evidence makes the ultrasound process more efficient than ozonation and addresses further studies for sonolysis optimisation as pretreatment for solid waste anaerobic digestion.

Kinetics of Biohydrogen Production from Ozonated Palm Oil Mill Effluent Using C. butyricum and C. acetobutylicum Co-Culture

Kinetics of mesophilic biohydrogen production from ozone-pretreated palm oil mill effluent (POME) using C. butyricum and C. acetobutylicum co-culture was investigated. All experiments were setup in 0.5-L batch reactors under mesophilic condition (37°C), pH 6, and POME concentration of 5,000-30,000 mg COD L-1. At the concentration of 15,000 mg COD L-1, maximum hydrogen production yield for non-ozone pretreated POME and ozone pretreated POME were 318 and 122 mL g-1 CODremoved, respectively. Acetic and butyric acids were dominant fermentation products in liquid phase. Ozone-pretreatment of POME showed no significant improvement on the hydrogen production by the co-culture.