BackgroundMicrobial electrolysis cells (MECs) use bioelectrochemical reactions to remove organic contaminants at the bioanode and produce hydrogen gas at the cathode. High local pH conditions near the cathode can also be utilized to produce struvite from nutrient-rich wastewater. This beneficial aspect was investigated using lab-scale MECs fed with dewatering centrate collected at a local wastewater treatment plant. The main objective was to improve phosphorus recovery by examining various cathode configurations and electric current conditions.ResultsThe stainless steel mesh (SSM) cathode was relatively inefficient to achieve complete phosphorus recovery because struvite crystals were smaller (a few to tens of micrometers) than the open space between mesh wires (80 µm). As a result, the use of multiple pieces of SSM also showed a limited improvement in the phosphorus recovery up to only 68% with 5 SSM pieces. Readily available organic substrates were not sufficient in the dewatering centrate, resulting in relatively low electric current density (mostly below 0.2 A/m2). The slow electrode reaction did not provide sufficiently high pH conditions near the cathode for complete recovery of phosphorus as struvite. Based on these findings, additional experiments were conducted using stainless steel foil (SSF) as the cathode and acetate (12 mM) as an additional organic substrate for exoelectrogens at the bioanode. With the high electric current (>2 A/m2), a thick layer of struvite crystals was formed on the SSF cathode. The phosphorus recovery increased to 96% with the increasing MEC operation time from 1 to 7 days. With the high phosphorus recovery, estimated energy requirement was relatively low at 13.8 kWh (with acetate) and 0.30 kWh (without acetate) to produce 1 kg struvite from dewatering centrate.ConclusionsFor efficient phosphorus recovery from real wastewater, a foil-type cathode is recommended to avoid potential losses of small struvite crystals. Also, presence of readily available organic substrates is important to maintain high electric current and establish high local pH conditions near the cathode. Struvite precipitation was relatively slow, requiring 7 days for nearly complete removal (92%) and recovery (96%). Future studies need to focus on shortening the time requirement.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-017-0754-8) contains supplementary material, which is available to authorized users.

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Bioanode sensors utilizing exoelectrogenic bacteria can be used for real-time and in situ assessment of water quality.

Nitrogen pollution is a serious environmental challenge in natural water and thus selective ammonia separation in wastewater treatment is of great importance to decrease the nitrogen load to natural water systems. BipolarThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

ABSTRATBiological contact oxidation (BCO) process and biological aerated filter (BAF) process were applied to decentralized wastewater treatment. The performances of two biofilm systems were monitored under four hydraulic loadings and six aeration rates. Effluent COD, NH 4 + -N, SS concentrations were presented with respect to the hydraulic and organic loadings, as well as the effluent DO. If the water reuse criteria were to be achieved, a maximum hydraulic and organic loading of 12.0 m 3 /d and 2.0 kg COD/(m 3 ·d), as well as a minimum effluent DO of 4.0 mg/L could be applied, respectively. Then kinetic analysis was carried out to describe the COD removal in two processes; for BAF there was: S e =S 0 e -0.639t /(1+1.035t); and for BCO, S e =S 0 [(1+0.947t) (1+1.242t)]. The correlation analysis showed that the two models could predict the effluent water quality based on the hydraulic retention time (HRT), so the appropriate hydraulic loading for certain effluent water quality could be determined. The two models could be applied to wastewater treatment practice.