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Owing to the high demand of petroleum and petrochemical products, refineries, among the many industries that are set up worldwide, are of special importance. Wastewater generated from such industrial activities, however, contains toxic compounds that are of environmental concern. Due to the presence of highly recalcitrant organics present in refinery wastewater, treatment prior to its discharge into the environment and water bodies in order to meet certain acceptable discharge limits is imperative. Petroleum refineries unavoidably discharge a large volume of wastewater mainly with high chemical oxygen demand (COD). Low‐cost biological wastewater treatment methods are reported to show excellent COD removal efficiency from wastewater but have their own drawbacks. Hence, advanced integrated approaches are of new interest in this field. This review focuses on emerging technologies, in particular bioreactor configurations for petroleum wastewater treatment. It further discusses some future perspective in hybrid/integrated systems for treating PRWW. [ABSTRACT FROM AUTHOR]

Refinery wastewater treatment was performed using a novel submerged tubular ceramic membrane bioreactor (STMBR) with the oleaginous hydrocarbonoclastic bacterium Rhodococcus opacus. A membrane‐based flux study with the STMBR was carried out to assess the performance of the tubular ceramic membrane. Continuous experiments with the STMBR achieved a maximum chemical oxygen demand (COD) removal of 84 %, with an average flux of 0.4 × 10−3 m3m−2s−1. To further enhance the COD removal efficiency, two STMBR were operated under the optimum conditions. Complete COD removal along with 2.98 g L−1 biomass growth was achieved during two‐stage STMBR operation. Furthermore, a toxicity assessment of the permeate water established its reuse potential. [ABSTRACT FROM AUTHOR]

• Biological removal of heavy metals by sulfate reduction using carbon monoxide (CO) as the carbon source was evaluated. • More than 90% heavy metal removal was obtained at low initial metal concentrations. • Heavy metals at high initial concentration affected both CO utilization and sulfate reduction. • Metal removal mechanism involved bioprecipitation due to sulfide produced from sulfate reduction. This study investigated the removal of heavy metals by biological sulfate reduction using CO as the sole carbon and energy source. The effect of different heavy metals, viz. Cu, Zn, Cd and Pb at initial concentrations in the range 5–100 mg/L on their respective removal was studied. Maximum removal efficiency was obtained with Cu as sulfate reduction was mostly unaffected in the presence of this metal; more than 60% sulfate reduction could be achieved even at a high metal concentration of 100 mg/L of Cu. Among these metals, Pb showed very strong inhibitory effect on sulfate reduction and CO utilization by the anaerobic biomass. Thus, heavy metal removal by sulfate reduction in turn depended on CO utilization efficiency by the anaerobic biomass. Field-emission scanning electron microscopy microscopy (FESEM) with energy dispersive X-ray spectroscopy (EDX) and fourier transform infrared spectroscopy (FTIR) spectra of the metal containing biomass confirmed that the bioprecipitates produced during the experimental study primarily consisted of the metal sulfides. This study has significant implications towards biological treatment of sulfate rich heavy metal containing wastewaters using CO as the carbon and energy source. [ABSTRACT FROM AUTHOR]

This study evaluated the performance of a continuously operated laboratory scale anaerobic rotating biological contactor (An-RBC) reactor at 24 h and 48 h residence time (RT) for heavy metal removal from synthetic wastewater under sulfate reducing condition. A maximum removal of Cu(II) (97%) followed by Cd(II) (90%) and more than 77% removal in case of the other metals, viz Pb(II), Fe(III), Zn(II) and Ni(II) were obtained for a maximum inlet metal concentration in the range 50–175 mg/L at 48 h RT. Metal loading rates greater than 3.64 mg/L·h in case of Cu(II) and 1.87 mg/L·h, in case of Fe(III), Pb(II), Ni(II), Zn(II) and Cd(II) are toxic and inhibitory to SRB activity and are therefore, detrimental to the performance of the An-RBC reactor. The metal removal values were slightly reduced at 24 h RT and the heavy metal removal was in the order: Cu > Cd > Pb > Fe > Zn > Ni at both the RTs. Sulfate removal results further confirmed that the heavy metal removal is due to sulfide generation in the reactor system. Field emission scanning electron microscopy (FESEM) images clearly revealed the immobilized sulfate reducing bacteria (SRB) onto the support material. Hence, this study demonstrated an excellent potential of the An-RBC reactor for treating metal containing wastewater even at high inlet concentration. [ABSTRACT FROM AUTHOR]

Microbial precipitation of heavy metals by sulfate reducing bacteria (SRB) through sulfate reduction as corresponding sulfides is being seen as a promising technique for the treatment of metal contaminated wastewater. SRB based bioprocesses are more attractive compared with chemical process owing to their low cost, very high removal and recovery of metals even at low initial concentration from wastewater. Both passive and active biological treatment systems are regarded as the most promising and potential treatment systems for a wide variety of metallic wastewater. These bioreactor systems offer more compact design, ease of performance and efficient control. However, there is limited information available on sulfidogenic bioreactors in the literature for a better understanding of the treatment system involving SRB. This is particularly important for scaling up of the potential of these systems. Hence, in this article, the highlights of different reactors (passive and active) used for treating sulfate and metal containing wastewater, factors affecting the process parameters, effect of different electron donors, merits and demerits of various reactors are emphasized. [ABSTRACT FROM AUTHOR]

This study evaluated the potential of the biosurfactant-producing yeastCandida bombicolain treating wastewater containing fats and oils from a dairy industry in a laboratory scale bioreactor. The dairy wastewater contains high chemical oxygen demand (COD) (2,480 mg/L) and fats and oils (407 mg/L) and was supplemented with sugarcane molasses (1% w/v) and yeast extract (0.1% w/v) to support the growing yeast in batch, fed-batch, and continuous operations. The yeast was able to remove fats and oils completely (more than 95% COD removal) under batch and continuous operation. The study suggested that wastewater containing high fats and oils can be efficiently treated usingC. bombicola. [ABSTRACT FROM PUBLISHER]

Biodegradation of phenol by predominantly Pseudomonas species isolated from a sewage wastewater treatment plant was investigated in batch shake flasks. Phenol with a lower concentration of 100 mg/L was degraded in 10 h and a highest of 800 mg/L in 69 h. The phenol degradation rate was observed to vary largely with the concentrations of phenol used and was found to be less than 10 mg/L/h at both the extremes of the initial concentrations. The degradation kinetics was found follow the three half-order kinetic model with the regression greater than 0.97. The specific substrate utilization rates of the culture at various initial phenol concentrations were fitted to modified substrate inhibition kinetic models of Edward, Haldane, Luong, Han--Levenspiel and Yano--Koga. Among these models the Edward was found to fit the data well with a minimum Root Mean Square error value of 0.0039. [ABSTRACT FROM AUTHOR]

The effects of initial dye concentration and disc rotation speed were studied on the performance of a continuously operated rotating biological contactor (RBC) reactor in decolourising an azo dye containing synthetic wastewater, employing the statistically planned 2k full factorial design of experiments. While the initial dye concentration in the study varied between 50 mg/l and 100 mg/l, the disc rotation speed ranged from 5 rpm to 11 rpm. The RBC with a hydraulic retention time of two days showed steady state dye decolourisation efficiency of more than 92% in all the experimental runs. Statistical analyses in the form of Analysis of Variance (ANOVA) and significance test of factors revealed that the main effects of both the factors were highly significant (P < 0.05) on the performance of the RBC and the effect of initial dye concentration was, however, negative and more compared to that of the disc rotation speed. [ABSTRACT FROM AUTHOR]

Acid mine drainage (AMD) is a serious environmental hazard in many countries with historic or ongoing mining industries. Biological sulfide precipitation is an emerging technique for both removal and recovery of heavy metals from such wastewater. This study demonstrated heavy metal removal and recovery from synthetic wastewater containing Cd2+, Cu2+, Fe3+, Ni2+, Pb2+ and Zn2+ using two continuously operated sulfidogenic anaerobic inverse fluidized bed reactors (referred as R1 and R2) supplied with an influent of pH 7.0 and 3.0, respectively. In case of R1, more than 95% metal removal efficiency was achieved for all the metals except for Fe3+ (90%) and Ni2+ (85%), and in case of R2 the removal was more than 90% for all the metals except with Fe3+ (88%) and Ni2+ (82%). The metals were subsequently recovered in the form of metal nanopowder from the reactor bottom and equalizer, and the metal recovery was in the order: Cu > Pb > Cd > Zn > Ni > Fe. However R1 yielded a good recovery percentage (50–65%) of the metals in comparison with the reactor supplied with influent of pH 3.0 (46–55%). The presence of immobilized sulfate reducing bacteria onto the support material in the bioreactors were identified using field emission scanning electron microscopy. The size and shape of the biometal nanoparticles were confirmed using field emission transmission electron microscopy, which revealed their excellent potential for industrial application. This study demonstrates successful recovery of metal sulfides in the form of nanoparticles using IFBR. • High metal removal efficiency is achieved by biological sulfate reduction. • Reactors run at influent pH 7.0 and 3.0 showed very high recovery of metals. • Copper showed best removal and recovery among all the metals tested. • Recovered metal nanopowder has reuse potential in industries. [ABSTRACT FROM AUTHOR]

Wastewater from biomass gasification chiefly contains monocyclic (MAHs) and polycyclic aromatic hydrocarbons (PAHs) that are generated by wet scrubbing process of raw synthetic gas during its cleaning process. These MAHs and PAHs are well-known as toxic, mutagenic, and carcinogenic agents which need to be removed prior to their release into the environment. The present study evaluated the potential of an up-flow packed bed bioreactor (UFPBBR) with immobilized Rhodococcus opacus onto biochar loaded polyurethane foam (PUF) as the packing material for treating biomass gasification wastewater (BGWW). Initially, the bioreactor was operated utilizing only PUF as the support material and a maximum COD removal of 81 ± 2.65% was achieved with 1820 mg L−1 of influent COD concentration and 24 h of HRT. Using biochar loaded PUF as the support material; more than 95 ± 1.27% of COD removal was attained under the same COD loading condition and HRT. Furthermore, the wastewater was detoxified to 96.2% demonstrating the ability of UFPBBR system using the novel biochar based bio-support material for biomass gasification wastewater treatment. Image 1 • Continuous treatment of biomass gasification wastewater using R. opacus is reported. • Biochar loaded polyurethane foam is an excellent bio-support material. • More than 99% toxicity removal from the wastewater could be achieved. • Stable performance is achieved even at low inlet loading and shock loading conditions. [ABSTRACT FROM AUTHOR]

• Construction of a superior Triacylglycerol (TAG) producing mutant BM985. • Simultaneous 88% COD removal by BM985. • Maximum of 68% TAG of dry cell weight (DCW) achieved under optimized conditions. • Production of commercial biodiesel grade fuel. Biofuel from bacterial lipids like triacylglycerol (TAG) is known to alleviate difficulties encountered in production of first (1 G), second (2 G) and third generation (3 G) biofuels. Rhodococcus opacus converts glucose into TAG, a biodiesel precursor, by using intermediates in the Kennedy pathway and specific PAP2 enzymes. The elucidation of genes involved, their functions and operational parameters is incomplete. Consequently, we have constructed a PAP2 over-expressing improved variant Rhodococcus opacus BM985 (BM985), optimized and evaluated its parameters for maximizing biodiesel production using synthetic dairy wastewater (SDWW) as the primary medium. Post application of optimization tools, we witnessed an impressive spike in TAG from 34.5% to 68% TAG/dry cell weight (DCW) content in BM985 cells at reactor level – a 1.98-fold increment compared to WT together with a lower BM985 biomass yield (0.76 g/g) but significant biomass concentration (3.7 g/L DCW). BM985 was effective in treating synthetic dairy wastewater with a chemical oxygen demand (COD) removal of ˜88% as compared to 65% by wild-type (WT). The fatty acid compositions obtained and thus the biodiesel properties such as cetane number, iodine number, osmotic stability etc. from BM985 strongly support the potential of BM985 as an alternative source for biofuel production and for DWW treatment. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Different bioreactors evaluated for refinery wastewater treatment by R. opacus. • Continuous operation mode with membrane cell recycle proved for better efficiency. • Low cost ceramic based tubular membrane was used for cell separation. • Hydrothermal liquefaction of biomass for suitable bio-fuel applications. Abstract Rapid consumption of fossil fuels has led to the search for alternative energy sources. Bio-fuels as an alternative energy source require cheap and abundantly available substrates to keep the economics of the production process low. The present study was therefore focused on utilizing raw refinery wastewater by the oleaginous bacterium Rhodococcus opacus for converting it into bio-oil via hydrothermal liquefaction of the lipid rich biomass produced during the treatment process. For treating the wastewater, different operating modes using a bioreactor were evaluated including batch, fed-batch, sequential batch, continuous and continuous with cell recycle using low cost tubular ceramic membrane. Among the different strategies, the continuous cell recycle system proved efficient in terms of complete removal of chemical oxygen demand (COD) (99%) and high lipid production (86%, w/w) at a hydraulic retention time (HRT) of 16 h (dilution rate of 0.06 h−1). Furthermore, the residual bacterial biomass from the bioreactor was treated by HTL to produce bio-oil which showed excellent bio-fuel properties. This study demonstrated the application of R. opacus for simultaneous wastewater treatment and production of bio-oil for energy application. [ABSTRACT FROM AUTHOR]

The use of fungal species to remove organic and inorganic pollutants from wastewater has shown to be a good alternative to traditional wastewater treatment technologies. Fungal pellets are well settling aggregates formed by self-immobilization. Their use in bioreactors is promising as it avoids the practical and technical difficulties usually encountered with dispersed mycelium. This review presents the mechanisms involved in the formation and growth of fungal pellets as well as the different factors that influence the stability of the pellets. The various types of fungal pelleted bioreactors that are used for wastewater treatment, their configuration, design and performance are reviewed. A summary of the different organic and inorganic pollutants that have been treated using fungal pelleted reactors, from dyes to emergent pollutants such as pharmaceuticals, is discussed from an application view-point. The operational issues such as bacterial contamination and longevity of this bioprocess under non-sterile conditions, as well as the reuse of fungal pellets are also encompassed in this review. [ABSTRACT FROM AUTHOR]

The non-linear complex relationships among the process variables in wastewater and waste gas treatment systems possess a significant challenge for real-time systems modelling. Data driven artificial intelligence (AI) tools are increasingly being adopted to predict the process performance, cost-effective process monitoring, and the control of different waste treatment systems, including those involving resource recovery. This review presents an in-depth analysis of the applications of emerging AI tools in physico-chemical and biological processes for the treatment of air pollutants, water and wastewater, and resource recovery processes. Additionally, the successful implementation of AI-controlled wastewater and waste gas treatment systems, along with real-time monitoring at the industrial scale are discussed. [Display omitted] • Advances of AI techniques in wastewater and waste gas treatment discussed. • ANN is widely used AI technique for better accuracy with non-linear data. • Optimization of treatment processes through integrated AI and ML techniques is presented. • Implementation of AI techniques are discussed. [ABSTRACT FROM AUTHOR]

• A self-regenerable oxygen system for biological removal of ammonium is reported. • NH 4 + removal efficiency strongly depends on microalgal photosynthesis and gas transfer. • Nitrogen concentration up to 82.5 mg/L favors nitrification by microalgae-bacterial consortia. • Combined mechanistic and empirical modeling revealed clear insight into N dynamics and DO profile. This study investigated self-regenerable oxygen system using microalagae-bacterial consortium for ammonium removal from wastewater and its kinetic modeling based on a combined mechanistic and empirical approach. By mechanistic modeling using a simple microalgal-bacterial Monod model, based on algal growth due to NH 4 +, NO 3 − and NO 2 −, the nitrogen and DO profiles were accurately predicted under different nitrogen conditions (low, medium, and high NH 4 + concentrations). The mathematical modeling results showed that sufficient oxygen was available for nitrification at low initial NH 4 + ammonium concentration levels, even when dual nitrogen substrate (NH 4 +–NO 2 −, NH 4 +–NO 3 − or NO 2 −–NO 3 −) or all three in combination (NH 4 +–NO 2 −–NO 3 −) were used, compared with high initial ammonium concentration levels. The DO profile was successfully used to monitor N transformation and N uptake in the PSBR based on net O 2 uptake rate, O 2 production rate, and O 2 saturation profile. By empirical modeling of the data obtained, the actual O 2 produced by microalgae with the different N species was calculated based on N mass balance and empirical equations. The empirical model further revealed that low NH 4 + concentration levels (up to 82.5 mg N/L) favored successful nitrification due to the sufficient production of O 2 in the system. However, NH 4 + concentration in the range 82.5–132.5 mg N/L affected the nitrification efficiency due to insufficient O 2 produced in the system, whereas high ammonium concentration results in nitritation/partial nitrification due to the high demand of O 2 by AOB and inhibition in the growth of NOB. [ABSTRACT FROM AUTHOR]

This study investigated utilization of refinery wastewater containing complex hydrocarbons as the sole substrate for lipid-rich biomass production by Rhodococcus opacus in batch system followed by its kinetic modeling. The effect of different initial chemical oxygen demand (COD) concentrations of the wastewater in the range 2.5–4.5 g L−1 was examined on biomass growth, COD utilization and lipid production by R. opacus. Almost complete utilization (96.8%) of COD present in the wastewater was achieved for an initial COD concentration of 2.5 g L−1 and the value decreased to 90% and 75% for 3.5 g L−1and 4.5 g L−1COD concentrations, respectively. Moreover, a maximum lipid production of 1.3 g L−1 was obtained for an initial COD concentration of 3.5 g L−1. The results of COD utilization by the bacterium were further fitted to substrate utilization kinetic models reported in the literature, which matched well with the Logistic model. Modified Gompertz model best fitted the kinetic data on biomass growth and lipid production by the bacterium. Whereas R. opacus biomass specific growth was found to be inhibited at a high COD concentration of the wastewater, Haldane model predicted the experimental specific growth rate values with a very high determination of coefficient (R2) value of more than 0.99. All these results suggest that refinery wastewater can serve as the sole substrate for lipid-rich biomass production by R. opacus , thereby adding value to the wastewater treatment process. Image 1 • Kinetics of refinery wastewater utilization and lipid-rich biomass production by Rhodococcus opacus are reported. • High concentration of organics inhibited biomass growth and lipid production. • Modified Gompertz model accurately described the biomass growth. • Experimental specific COD utilization rates are close to the Haldane model predicted values. • Estimated values of bio-kinetic model parameters indicate scale up potential of the process. [ABSTRACT FROM AUTHOR]

Microalgae based microbial fuel cells are efficient systems to remove nitrogen, phosphorous and CO 2 from wastewater, to produce bioelectricity and value-added products from microalgal biomass. Microalgae can be used in MFCs as algae assisted cathode systems, microbial carbon capture cells or sediment microbial fuel cells as well as photosynthetic microalgae microbial fuel cell. These MFCs are shown efficient for CO 2 capture with a low risk of carbon emission, N and P removal via symbiotic interactions of microalgae-bacteria consortia in wastewater treatment along with power generation. The oxygen production by microalgae during the light period reduces the need for external oxygen supply for cathodic reactions, which is advantageous for reducing the aeration cost, as otherwise power needs to be supplied for mechanical aeration. Utilization of algal biomass harvested from the cathodic compartment requires a pretreatment in a biorefinery concept. This still remains a major drawback, but current advances towards the choice of a biofilm on the cathode allow for further recovery of value-added products from algal biomass. Alternatively, the algal biomass can be utilized as the sole feedstock in the anodic compartment. This paper reviews the application of algae based microbial fuel cells for bioelectricity production, mainly focusing on the use of algae in the cathodic compartment, microalgae in the anodic compartment and the main interactions between the compartments affecting the bioelectricity production. Image 1 • Photosynthetic aeration by microalgae can replace conventional aeration in MFCs. • PAMFCs are well-suited for electricity production without mechanical aeration. • Use of microalgae in MFCs improves nitrogen, phosphorous and CO 2 removal rates. • Microalgae can be effectively used as a substrate for the anodic compartment. [ABSTRACT FROM AUTHOR]

• Carbon monoxide fed gas lift reactor is well suited for treating sulfate rich wastewater. • High sulfate removal obtained for low influent sulfate and high inlet CO concentrations. • Artificial neural network based model successfully predicted bioreactor performance. • Iron nanoparticle addition significantly improved the process efficiency. This study evaluated biodesulfuruization of sulfate containing wastewater using CO as the only carbon substrate in a gas lift bioreactor. The effect of hydraulic retention time (HRT), sulfate loading and CO loading rates on sulfate reduction and CO conversion was examined, and 72 h HRT proved to be best for achieving maximum sulfate reduction and CO utilization (97.2% and 88.9%, respectively). The CO utilization was nearly 80% at the beginning of the reactor operation, which reduced later due to increase in the inlet CO concentration in the third phase of bioreactor operation. Artificial neural network based model was successfully described to predict the performance of the system using Levenberg-Marquardt (LM) algorithm with twelve number of neurons. Steady state experimental values of sulfate reduction obtained using the gas lift bioreactor accurately matched well with the values predicted by the ANN model. Furthermore, addition of biologically synthesized iron nanoparticles using green tea extract significantly improved the bioreactor performance towards sulfate rich wastewater treatment with CO, particularly under high sulfate loading condition. [ABSTRACT FROM AUTHOR]

In this study, a moving bed biofilm reactor was used for biodesulfuruization using CO as the sole carbon substrate. The effect of hydraulic retention time (HRT), sulfate loading rate and CO loading rate on sulfate and CO removal was examined. At 72, 48 and 24 h HRT, the sulfate removal was 93.5%, 91.9% and 80.1%, respectively. An increase in the sulfate loading reduced the sulfate reduction efficiency, which, however, was improved by increasing the CO flow rate into the MBBR. Best results in terms of sulfate reduction (>80%) were obtained for low inlet sulfate and high CO loading conditions. The CO utilization was very high at 85% throughout the study, except during the last phase of the continuous bioreactor operation it was around 70%. An artificial neural network based model was successfully developed and optimized to accurately predict the bioreactor performance in terms of both sulfate reduction and CO utilization. Overall, this study showed an excellent potential of the moving bed biofilm bioreactor for efficient sulfate reduction even under high loading conditions. Image 1 • Carbon monoxide (CO) fed MBBR is highly suited for biological sulfate reduction. • Reactor showed stable performance towards both sulfate reduction and CO utilization. • HRT and CO sulfate ratio significantly affected the reactor performance. • Neural network modelling accurately predicted the bioreactor performance. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs), including naphthalene, phenanthrene and fluoranthene are commonly found in wastewaters from refineries and biomass gasification industries. This study investigated the simultaneous biodegradation of these PAHs along with lipid accumulation by Rhodococcus opacus in a ternary substrate system. A 2 3 full factorial design of experiments was employed with the three PAHs at two different levels by varying their initial concentrations in the range 50–200 mg L −1 each. A maximum removal of 91.6%, 82.3% and 80.7% was achieved for naphthalene, phenanthrene and fluoranthene, respectively. The individual effect of PAH concentration was found to be more significant than 2-way and 3-way interaction effects on their degradation. PAH biodegradation efficiency in the mixture was mainly affected by initial concentration and aromatic complexity of the PAHs. Identification of the PAH degradation metabolites was carried out using LC-MS analysis, which clearly revealed that the PAHs were degraded primarily via the ortho/para pathway. This study demonstrates the potential utility of R. opacus for bioremediation and industrial wastewater treatment. [ABSTRACT FROM AUTHOR]

This study examined the valorization of biomass gasification wastewater (BGWW) for lipids accumulation by Rhodococcus opacus and potential biodiesel application. Using synthetic mineral media based BGWW, the bacterium accumulated a maximum 65.8% (w/w) of lipids. 10% (v/v) inoculum size showed a more positive effect than 5% (v/v) inoculum size on both the chemical oxygen demand (COD) removal and lipid accumulation by R. opacus . Using the raw wastewater (untreated), the bacterium accumulated 54.3% (w/w) lipid with a wastewater COD removal efficiency of 64%. However, these values were further enhanced to 62.8% (w/w) and 74%, respectively, following supplementation of the wastewater with mineral salt media in the ratio 4:1. 1 H and 13 C nuclear magnetic resonance (NMR) spectroscopy analyses of the accumulated lipids revealed the presence of more saturated fatty acids than unsaturated fatty acids. Thermogravimetric analysis (TGA) of the accumulated lipids showed four thermal decomposition regions each with a good stability. Transesterification of the bacterial lipids to biodiesel and its properties revealed a very good potential of the strain for the production of biodiesel from PAH containing wastewater. [ABSTRACT FROM AUTHOR]