Anaerobic Co-Digestion of Oil Sludge with Corn Stover for Efficient Biogas Production

Unleashing synergistic potential of microbially enhanced anaerobic co-digestion of petroleum refinery biosludge and yard waste: Impact of nutrient balance and microbial diversity

Petroleum refinery sludge, an egregious solid residue generated from the wastewater treatment plants poses an environmental hazard owing to its intricate hydrocarbon composition, necessitating competent treatment for secure disposal. The study proposes a green solution through anaerobic co-digestion of nitrogen-rich petroleum refinery sludge (PS) with carbon-rich yard waste (YW), balancing the nutrients and moisture content for efficient microbial proliferation. Using Central Composite Design-Response Surface Methodology, 1 L batch experiments were conducted with varying carbon/nitrogen (C/N) ratios and pH to achieve maximum biogas yield within 50 days of co-digestion. However, the sluggish biogas recovery (40%) indicated a slow rate-limiting hydrolysis, necessitating pretreatment. Feedstock incubation with Bacillus subtilis IH1 strain, isolated from the microbially-enriched PS, at 108 colony forming units (CFU) per mL for 5 days maximized the soluble chemical oxygen demand and volatile fatty acids by 2.2 and 1.4 folds respectively compared to untreated feedstock. Scale-up Bacillus subtilis aided co-digestion studies further augmented biogas by 76% against untreated monodigestion of PS with significant total petroleum hydrocarbons, emulsions, and lignocellulosic degradation. Further identification of major organic pollutants in the batch digestate revealed significant degradation of the toxic organic hydrocarbon pollutants apotheosizing the efficacy of the synergistic sustainable technique for the management of PS. ENVIRONMENTAL IMPLICATION: The effluent treatment plants (ETPs) of petroleum refining industries generate sludge which is a complex mixture of petroleum hydrocarbons, oil-water (O/W) emulsions and heavy metals. These petroleum hydrocarbon constituents can be linear/cyclic alkanes, polyaromatics, resins and asphaltenes, whose intricate composition is reportedly carcinogenic, cytogenic and mutagenic, classifying it as hazardous waste. Biological treatment of these sludge through anaerobic digestion leads to utilization of petroleum hydrocarbons with subsequent energy recovery. Co-digestion of these sludge with competent co-substrates leads to nutrient balance, diverse microbial proliferation and toxicant dilution. Microbially aided co-digestion further augments methane rendering a digestate with utmost pollutant degradation.

Experimental and kinetic studies of biogas production from petroleum oily sludge by anaerobic co-digestion with animals’ dung at thermophilic conditions

Anaerobic co-digestion technology is widely used for biogas generation from organic wastes. In this study, co-digestion of petroleum oily sludge (POS) for biogas production in bench-scale anaerobic digesters at thermophilic conditions was investigated. The effects of inoculum type on the biogas production were considered. Three types of inoculums were examined individually for the co-digestion of POS which were; poultry manure, cattle manure, and cow dung. The results revealed that the biogas production from poultry manure, cattle manure, and cow dung exceeded its production from uninoculated POS by 64.6, 20.94 and 6.1% respectively. Effect of C/N on the co-digestion process was also considered in this study. Modified Gompertz model was applied to describe the kinetic of the co-digestion process. The predicted and experimental results of biogas generation were fitted well with coefficients of determination > 0.96 indicating appropriate conditions of the co-digestion process. Statistical analysis was performed to estimate if there were significant differences in terms of cumulative biogas yield. A significance level value of < 0.05 was obtained.

Petroleum sludge treatment and disposal techniques: a review

Petroleum sludge is a solid emulsified waste and contaminant commonly produced in the petroleum industry. In the recent past, there has been increased business growth in the oil sector, resulting in increased volumes of oily sludge characterized by high viscosity and toxicity. Therefore, sludge treatment before discarding is extremely necessary. This review seeks to highlight various conventional and evolving approaches in the treatment, recovery, and disposal of petroleum sludge and assess their suitability under various conditions.

Materials and energy recovery from oily sludges removed from crude oil storage tanks (tank bottoms): A review of technologies

Sludge and solids accumulating in crude oil storage tanks (referred as tank bottoms) reduces tank volume and requires periodic removal and disposal. Effective management of tank bottoms require considerations to reduce the toxicity of wastes and reduce potential environment impacts. This review compares alternative technologies for economical and environmentally beneficial management of oily sludges for recovery of hydrocarbons and energy with and without oil recovery. Management options with oil recovery include solvent extraction, centrifugation, surfactant oil recovery, and pyrolysis. Management options without oil recovery include incineration and anaerobic co-digestion. The selection of the appropriate technology depends on the characteristics of oily sludge, treatment capacity, as well as operation and maintenance costs. An efficient treatment can involve integration of different technologies for recovery of different oil fractions and to reduce energy demand. Technologies that utilize renewable energy (e.g., solar pyrolysis) can offset the high energy demand of pyrolysis process while recovering marketable products.