Review of technologies for biotreatment of refinery wastewaters: progress, challenges and future opportunities

A Brief Review of the Status of Low-Pressure Membrane Technology Implementation for Petroleum Industry Effluent Treatment

Low-pressure membrane technology (ultrafiltration and microfiltration) has been applied to two key effluents generated by the petroleum industry: produced water (PW) from oil exploration, a significant proportion being generated offshore, and onshore refinery/petrochemical effluent. PW is treated physicochemically to remove the oil prior to discharge, whereas the onshore effluents are often treated biologically to remove both the suspended and dissolved organic fractions. This review examines the efficacy and extent of implementation of membrane technology for these two distinct applications, focusing on data and information pertaining to the treatment of real effluents at large/full scale. Reported data trends from PW membrane filtration reveal that, notwithstanding extensive testing of ceramic membrane material for this duty, the mean fluxes sustained are highly variable and generally insufficiently high for offshore treatment on oil platforms where space is limited. This appears to be associated with the use of polymer for chemically-enhanced enhanced oil recovery, which causes significant membrane fouling impairing membrane permeability. Against this, the application of MBRs to onshore oil effluent treatment is well established, with a relatively narrow range of flux values reported (9−17 L·m−2·h−1) and >80% COD removal. It is concluded that the prospects of MBRs for petroleum industry effluent treatment are more favorable than implementation of membrane filtration for offshore PW treatment.

Bioaugmentation of treatment wetlands - A review

Bioaugmentation in the form of artificial mycorrhization of plant roots and bacterial inoculation has been successfully implemented in several fields including soil remediation or activated sludge treatment. Likewise, bioaugmentation seems a promising approach to improve the functioning of treatment wetlands, considering that natural mycorrhization has been detected in treatment wetlands and that bacteria are the main driver of contaminant degradation processes. However, to date, full scale implementation seems to be rare. This review synthesizes the effects of bioaugmentation on different types of treatment wetlands, to a large extent performed on a microcosm (<0.5 m²) or mesocosm scale (0.51 to 5 m²). While inoculation with arbuscular mycorrhizal fungi tended to show a positive effect on the growth of some wetland plants (e.g. Phragmites australis), the mechanisms underlying such positive effects are not well understood and the effects of upscaling to full scale treatment wetlands remain unknown. Bacterial inoculation tended to promote plant growth and pollutant degradation, but longer term data is required.

Refinery wastewater treatment via a multistage enhanced biochemical process

Petroleum refinery wastewater (PRWW) that contains recalcitrant components as the major portion of constituents is difficult to treat by conventional biological processes. An effective and economical biological treatment process was established to treat industrial PRWW with an influent COD of over 2500 mg L⁻¹ in this research. This process is mainly composed of internal circulation biological aerated filter (ICBAF), hydrolysis acidfication (HA), two anaerobic–aerobic (A/O) units, a membrane biological reactor (MBR), and ozone-activated carbon (O₃-AC) units. The results showed that, overall, this system removed over 94% of the COD, BOD_5, ammonia nitrogen (NH₄⁺-N) and phosphorus in the influent, with the ICBAF unit accounting for 54.6% of COD removal and 83.6% of BOD₅ removal, and the two A/O units accounting for 33.3% of COD removal and 9.4% of BOD₅ removal. The degradation processes of eight organic pollutants and their removal via treatment were also analyzed. Furthermore, 26 bacteria were identified in this system, with Proteobacteria and Acidobacteria being the most dominant. Ultimately, the treatment process exhibited good performance in degrading complex organic pollutants in the PRWW.

First approaches to valorizate fat, oil and grease (FOG) as anaerobic co-substrate with slaughterhouse wastewater: Biomethane potential, settling capacity and microbial dynamics

Anaerobic digestion (AD) is the biological preferred treatment applied to Slaughterhouse wastewaters (SWW) due to its effectiveness. The aim of the study is to investigate the effect of different percentages of fats, oil and grease (FOG) on biomethane production in anaerobic co-digestion with slaughterhouse wastewater using BMP tests under mesophilic conditions (35 °C). For this purpose, three percentages of FOG from 1% to 10% were tested. Biodegradability, biomethane production and the microbial population were studied. In addition, settling capacity has been evaluated at different conditions: i) before and after anaerobic co-digestion; ii) at different temperature 25 °C and 35 °C. The settling rates as well as the characterization of the digestate were recorded. Experimental results showed that all the co-digestion mixtures (FOG percentages = 1-10%) enhanced biomethane production and biodegradability compared to AD of sole SWW. The best conditions were achieved at 5-10% of FOG, showing biodegradability of 66-70% CODt_removal and specific biomethane productions of 562 and 777 mL_CH4·g^-1_CODsremoved, respectively. Regarding microbial dynamics, Eubacteria was reduced with the increase in %FOG but Acetate utilizing methanogens was increased. Regarding settling capacity, mesophilic temperatures (35 °C) increased the settling rate of digestate in 1.76 times and reduced the lag-phase to 0.92 min; obtaining a more concentrated sludge and leaving a clarified whose TSS represent only 8% of TS.

Microbial Metabolic Potential of Phenol Degradation in Wastewater Treatment Plant of Crude Oil Refinery: Analysis of Metagenomes and Characterization of Isolates

The drilling, processing and transportation of oil are the main sources of pollution in water and soil. The current work analyzes the microbial diversity and aromatic compounds degradation potential in the metagenomes of communities in the wastewater treatment plant (WWTP) of a crude oil refinery. By focusing on the degradation of phenol, we observed the involvement of diverse indigenous microbial communities at different steps of the WWTP. The anaerobic bacterial and archaeal genera were replaced by aerobic and facultative anaerobic bacteria through the biological treatment processes. The phyla Proteobacteria, Bacteroidetes and Planctomycetes were dominating at different stages of the treatment. Most of the established protein sequences of the phenol degradation key enzymes belonged to bacteria from the class Alphaproteobacteria. From 35 isolated strains, 14 were able to grow on aromatic compounds, whereas several phenolic compound-degrading strains also degraded aliphatic hydrocarbons. Two strains, Acinetobacter venetianus ICP1 and Pseudomonas oleovorans ICTN13, were able to degrade various aromatic and aliphatic pollutants and were further characterized by whole genome sequencing and cultivation experiments in the presence of phenol to ascertain their metabolic capacity in phenol degradation. When grown alone, the intermediates of catechol degradation, the meta or ortho pathways, accumulated into the growth environment of these strains. In the mixed cultures of the strains ICP1 and ICTN13, phenol was degraded via cooperation, in which the strain ICP1 was responsible for the adherence of cells and ICTN13 diminished the accumulation of toxic intermediates.

Evaluating Pre- and Post-Coagulation Configuration of Dissolved Air Flotation Using Response Surface Methodology

The effects of coagulation-dissolved air flotation (DAF) process configuration was studied on oil refinery wastewater. The configuration was done in two ways: acid-coagulation-DAF (pre-treatment) and acid-DAF-coagulation (post-treatment). Two different cationic and polymeric organic coagulants were employed in this study to compare their treatability performance with the two aforementioned configurations. All the coagulants applied before the DAF were found to be effective, with over 85% more contaminant removal efficiency than their post-treatment. Alum, being the most cost-effective coagulant, was then employed with response surface methodology (RSM) to obtain the optimum conditions. These include a coagulant dosage of 100 mg/L, air saturator pressure of 375 kPa and air–water ratio of 10% vol/vol corresponding to a desirability of 92% for the removal of oily pollutants from a local South Africa oil refinery’s wastewater. With the response quadratic models that were developed, the optimum conditions were tested experimentally, which were consistent with the models predicted results at a 95% confidence level.

Phragmites australis in combination with hydrocarbons degrading bacteria is a suitable option for remediation of diesel-contaminated water in floating wetlands

The presence of diesel in the water could reduce the growth of plant and thus phytoremediation efficacy. The toxicity of diesel to plant is commonly explained; because of hydrocarbons in diesel accumulate in various parts of plants, where they disrupt the plant cell especially, the epidemis, leaves, stem and roots of the plant. This study investigated the effect of bacterial augmentation in floating treatment wetlands (FTWs) on remediation of diesel oil contaminated water. A helophytic plant, Phragmites australis (P. australis), was vegetated on a floating mat to establish FTWs for the remediation of diesel (1%, w/v) contaminated water. The FTWs was inoculated with three bacterial strains (Acinetobacter sp. BRRH61, Bacillus megaterium RGR14 and Acinetobacter iwoffii AKR1), possessing hydrocarbon degradation and plant growth-enhancing capabilities. It was observed that the FTWs efficiently removed hydrocarbons from water, and bacterial inoculation further enhanced its hydrocarbons degradation efficacy. Diesel contaminated water samples collected after fifteen days of time interval for three months and were analyzed for pollution parameters. The maximum reduction in hydrocarbons (95.8%), chemical oxygen demand (98.6%), biochemical oxygen demand (97.7%), total organic carbon (95.2%), phenol (98.9%) and toxicity was examined when both plant and bacteria were employed in combination. Likewise, an increase in plant growth was seen in the presence of bacteria. The inoculated bacteria showed persistence in the water, root and shoot of P. australis. The study concluded that the augmentation of hydrocarbons degrading bacteria in FTWs is a better option for treatment of diesel polluted water.

Biological wastewater treatment (anaerobic-aerobic) technologies for safe discharge of treated slaughterhouse and meat processing wastewater

Slaughterhouse industry generates considerable amount of wastewater rich in proteins, lipids, fibres, and carbohydrates. Numerous technologies such as electrocoagulation, membrane separation, advanced oxidation, physico-chemical processes, and biological treatment have been implemented for reducing the concentrations of these compounds. Nevertheless, this review aims to provide extensive information solely on the biological treatment (anaerobic and aerobic) of slaughterhouse wastewater. The advantages of anaerobic treatment are excellent organic matter removal, less sludge production, low energy requirement, execution of higher loading rates, and considerable production of biogas. Aerobic treatment on the other hand is a less sensitive process, possess lower start-up period, and efficient nutrient removal process. Numerous case studies are described to bestow maximum understanding of the wastewater characteristics, kind of treatment employed, and complications involved in managing and treating of slaughterhouse effluent. Additionally, role of microbial community involved in the treatment of slaughterhouse waste is also discussed. Sequential anaerobic and aerobic reactors are also reviewed in order to present their advantages over single bioreactors. Intermittent sequencing batch reactor is a promising technology than other high rate digesters in the removal of carbon, nitrogen, and phosphorous.

Enhancement of oil field-produced wastewater remediation by bacterially-augmented floating treatment wetlands

Plants and bacteria individually as well as in synergism with each other hold a great potential to degrade a wide range of environmental pollutants. Floating treatment wetlands (FTWs) is an efficient and low-cost technology that uses the synergistic interaction between plant roots and microbes for in situ remediation of wastewater. The present study aims to assess the feasibility of FTW-based remediation of oil field-produced wastewater using an interaction between two plant species, Typha domingensis and Leptochloa fusca, in partnership with a consortium of crude oil-degrading bacterial species, Bacillus subtilis LORI66, Klebsiella sp. LCRI87, Acinetobacter Junii TYRH47, and Acinetobacter sp. BRSI56. All the treatments reduced contaminant levels, but T. domingensis, in combination with bacterial inoculation, exhibited the highest reduction in hydrocarbon (95%), COD (90%), and BOD content (93%) as compared to L. fusca. This combination maximally promoted increases in fresh biomass (31%), dry biomass (52%), and length (25%) of plants as well. This effect was further signified by the persistence of bacteria (40%) and considerable abundance (27%) and expression (28.5%) of the alkB gene in the rhizoplane of T. domingensis in comparison to that of L. fusca. The study, therefore, suggests that T. domingensis, in combination with bacterial consortium, has significant potential for treatment of oil field-produced water and can be exploited on large scale in FTWs.

Biostimulation of Indigenous Microbial Community for Bioremediation of Petroleum Refinery Sludge

Nutrient deficiency severely impairs the catabolic activity of indigenous microorganisms in hydrocarbon rich environments (HREs) and limits the rate of intrinsic bioremediation. The present study aimed to characterize the microbial community in refinery waste and evaluate the scope for biostimulation based in situ bioremediation. Samples recovered from the wastewater lagoon of Guwahati refinery revealed a hydrocarbon enriched [high total petroleum hydrocarbon (TPH)], oxygen-, moisture-limited, reducing environment. Intrinsic biodegradation ability of the indigenous microorganisms was enhanced significantly (>80% reduction in TPH by 90 days) with nitrate amendment. Preferred utilization of both higher- (>C30) and middle- chain (C20-30) length hydrocarbons were evident from GC-MS analysis. Denaturing gradient gel electrophoresis and community level physiological profiling analyses indicated distinct shift in community’s composition and metabolic abilities following nitrogen (N) amendment. High throughput deep sequencing of 16S rRNA gene showed that the native community was mainly composed of hydrocarbon degrading, syntrophic, methanogenic, nitrate/iron/sulfur reducing facultative anaerobic bacteria and archaebacteria, affiliated to γ- and δ-Proteobacteria and Euryarchaeota respectively. Genes for aerobic and anaerobic alkane metabolism (alkB and bssA), methanogenesis (mcrA), denitrification (nirS and narG) and N₂ fixation (nifH) were detected. Concomitant to hydrocarbon degradation, lowering of dissolve O₂ and increase in oxidation-reduction potential (ORP) marked with an enrichment of N₂ fixing, nitrate reducing aerobic/facultative anaerobic members [e.g., Azovibrio, Pseudoxanthomonas and Comamonadaceae members] was evident in N amended microcosm. This study highlighted that indigenous community of refinery sludge was intrinsically diverse, yet appreciable rate of in situ bioremediation could be achieved by supplying adequate N sources.