Abstract
Bio-electrochemical ammonium recovery (BEAR) can close the cycle between anthropogenic emission of reactive nitrogen and energy intensive nitrogen fixation in the Haber-Bosch process. BEAR is currently limited by the bio-electrogenic degradability of the treated wastewater. Here, we investigated the degradability of blackwater, hydrolyzed human urine, cow manure and pig manure as prospective wastewaters for BEAR in a standardized experimental design.We found that bio-electrochemical conversion efficiencies ranged from 63% (blackwater) to 42% (cow manure) and 41% (urine) to 26% (pig manure) after 5 days. These values correspond well with the relative VFA content of soluble COD for blackwater and cow manure, while additional compounds must have been converted for urine and pig manure.The degradability of blackwater and cow manure was sufficiently high to theoretically be able to remove all TAN already after < 0.5 d. The actual recovery potential (consisting of conversion efficiency and COD/TAN ratio) of pig manure was just high enough to remove all TAN. Human urine would require additional electron donor to remove all TAN in BEAR. Therefore, combining the maximum recovery potential with the relative VFA content of soluble COD can give a good estimate of the actual recovery potential of a wastewater.
Highlights
An increasing world population will require higher agricultural output and more fertilizer to sustain human food production [1]
Several wastewaters were investigated because of their high COD and total ammonia nitrogen (TAN) concentrations, which makes them attractive for bioelectrochemical ammonium recovery (BEAR). These wastewaters were: source separated human black water, hydrolyzed human urine, cow manure and pig manure. They were characterized in terms of solids, pH, predominant buffer components (TAN and inorganic carbon), total COD (CODt) and COD after paper filtration (CODf), vol atile fatty acids (VFAs) and acetate concentrations (Table 1)
All wastewaters contained more than 3 g/L of COD that may be converted into electricity
Summary
An increasing world population will require higher agricultural output and more fertilizer to sustain human food production [1]. Bio-electrochemical Systems (BESs) are sustainable technologies to recover ammonium (NH4+) as part of total ammonia nitrogen (TAN) at low energy cost [3,4]. In BESs, bio-degradable organic compounds in wastewaters are converted into electricity, thereby driving ammonium across a cation exchange membrane (CEM) and separating it from the wastewater. This separated TAN can be recovered from the cath olyte, i.e. by using a membrane distillation process [5,6]. While bioelectrochemical ammonium recovery (BEAR) provides an elegant solu tion to both pollutant removal and nutrient recovery, its key challenge lies in the production of sufficient electrical current to separate the TAN from the wastewater [4]. There fore, the ratio of charge of electrons as electricity over charge of ammonium loaded can be expressed as load ratio and give a good esti mate for expected TAN removal efficiency and threshold for optimal system operation [7]
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