Total petroleum hydrocarbon degradation by hybrid electrobiochemical reactor in oilfield produced water

An overview of in situ remediation for groundwater co-contaminated with heavy metals and petroleum hydrocarbons

Groundwater is an important component of water resources. Mixed pollutants comprising heavy metals (HMs) and petroleum hydrocarbons (PHs) from industrial activities can contaminate groundwater through such processes as rainfall infiltration, runoff and discharge, which pose direct threats to human health through the food chain or drinking water. In situ remediation of contaminated groundwater is an important way to improve the quality of a water environment, develop water resources and ensure the safety of drinking water. Bioremediation and permeable reactive barriers (PRBs) were discussed in this paper as they were effective and affordable for in situ remediation of complex contaminated groundwater. In addition, media types, technology combinations and factors for the PRBs were highlighted. Finally, insights and outlooks were presented for in situ remediation technologies for complex groundwater contaminated with HMs and PHs. The selection of an in situ remediation technology should be site specific. The remediation of complex contaminated groundwater can be approached from various perspectives, including the development of economical materials, the production of slow-release and encapsulated materials, and a combination of multiple technologies. This review is expected to provide technical guidance and assistance for in situ remediation of complex contaminated groundwater.

Saline wastewater treatment by bioelectrochemical process (BEC) based on Al-electrocoagulation and halophilic bacteria: optimization using ANN with new approach

ABSTRACTIn the present study, a bioelectrochemical reactor (BEC) was utilized to treat two types of real saline produced water (PW). BEC was designed based on the combination of electrocoagulation (EC) process with halophilic microorganisms, and it was assessed in terms of biodegradation of hydrocarbons. The effects of various operating parameters including the current density, electrical contact time (On/Off), hydraulic retention time (HRT), and total dissolved solids (TDS) at different levels on the chemical oxygen demand (COD) removal efficiency, settleability, and performance of isolated halophilic microorganisms were examined. Additionally, a novel neural network (ANN) approach modelling using adaptive factors was used to predict and optimize the effects and interactions between operating parameters during BEC process by predicting complicated mechanisms and variations associated with microorganisms. In addition, a new algorithm was developed for the sensitivity analysis to achieve the optimum operating conditions and obtain maximum efficiency in COD removal, sludge volume index (SVI), mixed liquor suspended solids (MLSS), and specific electrical energy consumption (SEEC), simultaneously. BEC was found to be significantly more effective at removing most hydrocarbons, particularly pristine and phytane. In addition, the results showed a significant improvement in settling ability of the biological flocs with average SVI of 91.5 mL/g and a size of 178.25 μm using BEC. Based on estimated operating costs and energy consumption, BEC was more cost-effective and efficient than other bioelectrochemical systems.

Modified bio-electrocoagulation system to treat the municipal wastewater for irrigation purposes

A modified biological-integrated electrocoagulation method was explored to treat municipal wastewater (MWW) for irrigation purposes. To use treated wastewater for irrigation purposes a wide range of contaminants removal was focused on in this study (turbidity, hardness, conductivity, TDS, TSS, chloride, Ammonia nitrogen, BOD, COD, and total coliform). Raw municipal wastewater (RMWW) was treated in a modified Bio-Electrocoagulation (BEC) cell. The cell was operated in a continuous flow mode and consisted of an electrocoagulation stage using aluminum (Al) electrodes followed by a bioremediation stage using a fixed bio-filter (BF), the design of the cell was further modified by the addition of a sand filter (SF). The effect of several parameters such as applied voltage (22, 26, and 30 V), inlet flow rate (1, 3, and 5 Lh^-1), and initial pH (pH 3, 5, 7, 7.4, and 9) was investigated to determine the optimum operating conditions for selected responses. The most effective operating conditions for the BEC were investigated for the different irrigation water quality (WQ) indicators. It was observed that pH 7.4 and 26 V provide maximum removal efficiency of contaminants at the flow rate of 1 Lh^-1. A fixed film BF plays a positive role to improve the degradation of contaminants after the EC unit up to 4% of NH₃-N, 9.3% of BOD, and 7.8% of COD. In addition, using the SF improved the turbidity removal to 42.6%. The WQ specifications of the treated MWW using the BEC cell were compared with the standard specifications for restricted and unrestricted agricultural irrigation water. The overall operating cost of MWW treatment for irrigation purposes by using a modified bio-integrated electrocoagulation method was 0.76 $m^-3.

Treatment of Produced Water in the Permian Basin for Hydraulic Fracturing: Comparison of Different Coagulation Processes and Innovative Filter Media

Produced water is the largest volume of waste product generated during oil and natural gas exploration and production. The traditional method to dispose of produced water involves deep well injection, but this option is becoming more challenging due to high operational cost, limited disposal capacity, and more stringent regulations. Meanwhile, large volumes of freshwater are used for hydraulic fracturing. The goal of this study is to develop cost-effective technologies, and optimize system design and operation to treat highly saline produced water (120–140 g/L total dissolved solids) for hydraulic fracturing. Produced water was collected from a salt water disposal facility in the Permian Basin, New Mexico. Chemical coagulation (CC) using ferric chloride and aluminum sulfate as coagulants was compared with electrocoagulation (EC) with aluminum electrodes for removal of suspended contaminants. The effects of coagulant dose, current density, and hydraulic retention time during EC on turbidity removal were investigated. Experimental results showed that aluminum sulfate was more efficient and cost-effective than ferric chloride for removing turbidity from produced water. The optimal aluminum dose was achieved at operating current density of 6.60 mA/cm2 and 12 min contact time during EC treatment, which resulted in 74% removal of suspended solids and 53–78% removal of total organic carbon (TOC). The energy requirement of EC was calculated 0.36 kWh/m3 of water treated. The total operating cost of EC was estimated $0.44/m3 of treated water, which is 1.7 or 1.2 times higher than CC using alum or ferric chloride as the coagulant, respectively. The EC operating cost was primarily associated with the consumption of aluminum electrode materials due to faradaic reactions and electrodes corrosions. EC has the advantage of shorter retention time, in situ production of coagulants, less sludge generation, and high mobility for onsite produced water treatment. The fine particles and other contaminants after coagulation were further treated in continuous-flow columns packed with different filter media, including agricultural waste products (pecan shell, walnut shell, and biochar), and new and spent granular activated carbon (GAC). Turbidity, TOC, metals, and electrical conductivity were monitored to evaluate the performance of the treatment system and the adsorption capacities of different media. Biochar and GAC showed the greatest removal of turbidity and TOC in produced water. These treatment technologies were demonstrated to be effective for the removal of suspended constituents and iron, and to produce a clean brine for onsite reuse, such as hydraulic fracturing.

Characterizing petroleum hydrocarbons deposited on road surfaces in urban environments

Petroleum hydrocarbons are a toxic pollutant group, primarily including volatile organic compounds (VOC), semi-volatile organic compounds (SVOC) and non-volatile organic compounds (NVOC). These pollutants can be accumulated on urban roads during dry periods and then washed-off by stormwater runoff in rainy days. Unlike heavy metals and polycyclic aromatic hydrocarbons, petroleum hydrocarbons have not received an equal attention in the field of stormwater pollutant processes. This paper investigated characteristics of VOC, SVOC and NVOC pollutant loads deposited on urban roads and their influential factors using a forward stepwise regression and PROMETHEE-GAIA analysis techniques. The results indicate that the loads deposited on urban roads were NVOC > SVOC > VOC. It is also noted that the degrees of factors in influencing petroleum hydrocarbons deposited on urban roads did not equal and their order was total solids > land use type > vehicular traffic > roughness of road surfaces. The research results also showed that petroleum hydrocarbons on urban road surfaces tend to be source limiting rather than transport limiting. These outcomes can contribute to petroleum hydrocarbons polluted stormwater management, such as treatment system design and stormwater modelling approach improvement.