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The objective of the present study was to investigate the effectiveness of spark plasma discharges on the inactivation of acid-producing bacteria (APB) and sulfate-reducing bacteria (SRB) in produced water. Tests were conducted in both static batch mode and once-through flow mode. The residual effect of plasma treatment was assessed by two different protocols: immediate incubation after plasma treatment and incubation after 24-h storage in a tank post-treatment. In the batch test, 10-min plasma treatment of water showed a total 3-log reduction of APB and 2-log reduction of SRB based on cfu/mL data in the case of clear produced water. In the once-through flow test, 2-log reduction of APB was observed in the case of clear produced water, whereas 1-log to 1.5-log reductions were observed in the case of darkly opaque produced water. The energy efficiency for the once-through flow test with APB for the opaque produced water was 1.7 kJ/L per 1-log reduction. UV radiation together with active plasma species produced by the spark discharge was instrumental in the inactivation of APB and SRB in both clear and dark produced water.

The objective of the present study was to investigate the feasibility of using spark type plasma discharges to provide a self-cleaning effect for filtration of produced water. A new co-axial electrode system was developed for the generation of spark discharges in high-conductivity produced water. The validation experiment was conducted with the spark-assisted self-cleaning (SASC) filtration system in both synthetic produced water and actual produced water at different total dissolved solids (TDS) and total suspended solids (TSS) levels and at three different flow rates of 0.126, 0.315, and 0.631 L/s (i.e., 2, 5 and 10 gpm). The pressure drop across the filter surface was measured over time. The pressure drop obtained without spark discharges increased consistently over time, often resulting in pump failure due to excessive pressure buildup at the pump. The pressure drop obtained with spark discharges was significantly smaller than those obtained without spark discharges. The present study sufficiently demonstrated the validity of the SASC filtration concept. The range of water properties that were shown to be treatable with the SASC filtration system using 10-in cartridge filter of 3- and 5-micron pores was TDS level ⩽50,000 mg/L and TSS level ⩽2500 mg/L.

The objectives of the present study were to test a new plasma-based method for bicarbonate removal in water produced from hydraulic fracturing for shale gas and to verify bicarbonate removal as a mechanism for mineral fouling prevention. The study employed dual hypotheses: (1) gliding arc plasma can reduce bicarbonate concentration of produced water to negligible levels, and (2) water without bicarbonate content is unable to cause mineral fouling in the form of calcium carbonate scale even in the presence of extremely high concentrations of calcium ions as is often found in produced water. The plasma treatment of produced water reduced the concentration of bicarbonate ions from a range of 684–778 ppm to zero. Subsequently, heat transfer fouling tests were conducted with water samples, where the concentration of bicarbonate ions varied from 0 to 500 ppm with a fixed concentration of calcium ions of 5000 ppm. The weight of mineral scale that accumulated on a heating element over time was determined. The present test results showed that no fouling was formed over 30 h on the heating element in the water without bicarbonate ions. This proof-of-concept study demonstrated that plasma treatment is capable of reducing the concentration of bicarbonate ions in produced water to a level where CaCO3 fouling can be prevented on a heat transfer surface. The plasma gliding arc may represent a new non-chemical fouling prevention method for the treatment of produced water.

The ability of a GA discharge to produce hydrogen peroxide (H 2 O 2 ), a potent oxidizer, was investigated to evaluate the optimum operational condition of the GA discharge for bacterial inactivation. The concentration of H 2 O 2 was measured in liquid phase, and its effective residual time was evaluated in a 200-W GA discharge system at different air and water flow rates. The concentration of H 2 O 2 was the highest at the least water flow rate. In addition, a 5-log reduction in the colony forming unit (cfu) number of E. coli was observed at a H 2 O 2 concentration of 100 mg/L in water.