Haiman Wang

A combined microbial desalination cell and electrodialysis system for copper-containing wastewater treatment and high-salinity-water desalination

A new concept for heavy metal removal by forming hydroxide precipitation using alkalinity produced by microbial desalination cell (MDC) was proposed. Four five-chamber MDCs were hydraulically connected to concurrently produce alkalinity to treat synthetic copper-containing wastewater and salt removal. There was nearly complete removal of copper, with a maximum removal rate of 5.07kg/(m3d) under the initial copper concentration of 5000mg/L (final pH of 7). The final copper concentration met the emission standard for electroplating of China (0.5mg/L, GB 21900-2008). XRD analysis indicated copper was precipitated as Cu2Cl(OH)3. The best performance of MDCs in terms of average power density, salt removal and COD removal rate achieved in stage 3 were 737.3±201.1mW/m2, 53.6±0.8kg/(m3d), and 1.84±0.05 kgCOD/(m3d) respectively. For purposes of water recovery, an electrodialysis (ED) system was presented based on in-situ utilization of generated electricity by MDCs as post-desalination treatment for salt effluent after sedimentation. The maximum discharging voltage of 12.75±1.26V at switching time (Ts) of 15min using a capacitor-based circuit produced a maximum desalination efficiency of 30.4±2.6%. These results indicated that this combined system holds great promise for real-world treatment of copper-containing wastewater and deep desalination of high-salinity-water.

Evaluation of an integrated continuous stirred microbial electrochemical reactor: Wastewater treatment, energy recovery and microbial community.

A continuous stirred microbial electrochemical reactor (CSMER) was developed by integrating anaerobic digestion (AD) and microbial electrochemical system (MES). The system was capable of treating high strength artificial wastewater and simultaneously recovering electric and methane energy. Maximum power density of 583±9, 562±7, 533±10 and 572±6 mW m(-2) were obtained by each cell in a four-independent circuit mode operation at an OLR of 12 kg COD m(-3) d(-1). COD removal and energy recovery efficiency were 87.1% and 32.1%, which were 1.6 and 2.5 times higher than that of a continuous stirred tank reactor (CSTR). Larger amount of Deltaproteobacteria (5.3%) and hydrogenotrophic methanogens (47%) can account for the better performance of CSMER, since syntrophic associations among them provided more degradation pathways compared to the CSTR. Results demonstrate the CSMER holds great promise for efficient wastewater treatment and energy recovery.

Cascade degradation of organic matters in brewery wastewater using a continuous stirred microbial electrochemical reactor and analysis of microbial communities.

A continuous stirred microbial electrochemical reactor (CSMER), comprising of a complete mixing zone (CMZ) and microbial electrochemical zone (MEZ), was used for brewery wastewater treatment. The system realized 75.4 ± 5.7% of TCOD and 64.9 ± 4.9% of TSS when fed with brewery wastewater concomitantly achieving an average maximum power density of 304 ± 31 m W m−2. Cascade utilization of organic matters made the CSMER remove a wider range of substrates compared with a continuous stirred tank reactor (CSTR), in which process 79.1 ± 5.6% of soluble protein and 86.6 ± 2.2% of soluble carbohydrates were degraded by anaerobic digestion in the CMZ and short-chain volatile fatty acids were further decomposed and generated current in the MEZ. Co-existence of fermentative bacteria (Clostridium and Bacteroides, 19.7% and 5.0%), acetogenic bacteria (Syntrophobacter, 20.8%), methanogenic archaea (Methanosaeta and Methanobacterium, 40.3% and 38.4%) and exoelectrogens (Geobacter, 12.4%) as well as a clear spatial distribution and syntrophic interaction among them contributed to the cascade degradation process in CSMER. The CSMER shows great promise for practical wastewater treatment application due to high pre-hydrolysis and acidification rate, high energy recovery and low capital cost.

Analysis of the effect of biofouling distribution on electricity output in microbial fuel cells

Single chamber air-cathode microbial fuel cells (MFCs) were operated for 6 months to demonstrate the impact of biofouling distribution on cathode performance. Total biofouling decreased the maximum power density by 38% from 892 ± 8 mW m−2 to 549 ± 16 mW m−2. Cleaning surface biofouling slightly enhanced the power density by 12%, but additional removing of the biofouling inside the catalyst layer further increased power output by 30% to 802 ± 14 mW m−2, indicating that inner biofouling aggressively inhibits cathode activity. Compared with surface biofouling, the inner biofouling clogged a portion of pores in the catalyst layer, which severely reduced oxygen permeability, conductivity and reaction sites. Consequently, the kinetic activity of the cathode was impaired as the exchange current density declined and the charge transfer resistance increased. Thus, it is shown that the biofouling within the catalyst layer plays a more crucial role for air cathodes over long-term operation.

Microwave-assisted synthesis of nitrogen-doped activated carbon as an oxygen reduction catalyst in microbial fuel cells

A nitrogen-doped activated carbon (NDAC) as a cathode catalyst in microbial fuel cells (MFCs) was synthesized by a microwave-assisted method using ammonium carbonate as a nitrogen source. The prepared NDAC showed a higher BET surface area of up to 1717.8 m2 g−1 and a total pore volume of 0.79 cm3 g−1. X-ray photoelectron spectroscopic analysis demonstrated that N was successfully doped on the surface of AC in three species, corresponding to pyrrolic N, pyridinic N and pyridine-N-oxide. Compared with untreated AC, the NDAC exhibited better electrocatalytic activity for the oxygen reduction reaction in rotating disk electrode tests, with a current density of 12.4 mA cm−2 at a set potential of −0.8 V (vs. SCE) (AC, 11.3 mA cm−2) and an electron transfer number of 3.14 (AC, n = 2.83). MFCs equipped with a NDAC cathode achieved a higher maximum power density of 471 ± 11 mW m−2 when fed with domestic wastewater, which was 1.3 times higher than that of the AC cathode. It also displayed long-term operation stability when dealing with real wastewater, indicating a promising cathode catalyst for MFCs towards practical applications.

Energy-positive nitrogen removal from reject water using a tide-type biocathode microbial electrochemical system

A tide-type biocathode microbial electrochemical system (TBMES) employing intermittent air accessible method was constructed for simultaneous carbon and nitrogen removal. The nitrification and denitrification processes occurred in cathode chamber were enhanced by raising frequency of catholyte feeding-draining process and lowering external resistance. At external resistance of 5Ω and frequency of 8cph, the TBMES removed 99.3±0.3% of COD and 57.7±1.1% of total nitrogen when treating synthetic medium with COD/N ratio of 3.0, concomitantly, a maximum power density of 10.6Wm-3 was achieved. Comparable performances were obtained for reject water treatment with a relatively lower COD/N ratio of 2.5, which were 88.6±1.3%, 53.2±3.8% and 8.9±0.2Wm-3 for COD removal, total nitrogen removal and maximum power density. The feeding-draining process consumed 14.3% of the total energy produced, and thus obviated energy-intensive aeration and achieved net energy output.

Simultaneous current generation and ammonia recovery from real urine using nitrogen-purged bioelectrochemical systems

Bioelectrochemical systems (BESs) offer a strategy for treating source-separated urine with current generation, but the high content of ammonia is still a challenge for sustainable maintenance of BESs due to ammonia inhibition. Therefore, an integrated BES setup was developed to overcome this problem by ammonia recovery. This setup, working in closed circuit mode with nitrogen purging (CN), allowed for the produced ammonia to be continuously channeled to an absorption bottle. In addition, control reactors in closed circuit (CC) or in open circuit mode (OC) were also run for comparison. A maximum power density of 310.9 ± 1.0 mW m−2 was obtained for the CN reactor, and 127.1 ± 0.9 mW m−2 was obtained for the CC reactor. Total nitrogen (TN) removal efficiency (84.9% ± 2.2%) from urine was considerably higher in the CN reactor than it was in the CC (29.7% ± 6.7%) or OC (30.0% ± 8.2%) reactor. In the CN reactor, 52.8% ± 3.6% of the TN was recovered in the form of NH3-N, with a NH3 recovery rate of 435.7 ± 29.6 gN m−3 d−1. The improved performance of the CN reactor was attributed to the mitigation of ammonia inhibition to the anode electro-activity. 16S rDNA sequencing showed that no Anammox and nitrifiers were detected on the anodes and cathodes. Overall, nitrogen purging provides the urine-fed BESs with a useful approach for maintaining the system performance by ammonia recovery.