Disruptions in loading and aeration impact effluent chlorine demand during biological greywater recycling

• Published in: Water research X 2021-05, Vol.11, p.100087-100087, Article 100087
• Main Authors: Ziemba, Christopher, Sharma, Pragnya, Ahrens, Theresa, Reynaert, Eva, Morgenroth, Eberhard
• Format: Article
• Language: English
• Subjects: Biologically activated membrane bioreactor (BAMBi); Chlorination; Decentralized; Gravity-driven membrane (GDM) treatment; Hand washing water; Permeate quality
• ISSN: 2589-9147; 2589-9147
• DOI: 10.1016/j.wroa.2020.100087

Greywater recycling systems designed for high-quality applications, such as hand washing, must deliver microbially safe and aesthetically acceptable water under the challenging operating conditions present where such systems are needed most urgently. As chlorination is the most popular strategy for reducing bacterial concentrations in greywater, understanding chlorination in the context of disruptive and challenging operation is essential to designing robust treatment. In this study, we have examined how disruptions through overall increased loading, interrupted aeration and increased ammonia loading have impacted the chlorine demand of the water produced by a greywater recycling system. We also presented concentrations of significant chemicals that contributed to this chlorine demand. The results indicate that a 1 d period with 8 times (8x) the normal design loading produced a peak chlorine demand of 0.74 mg Cl2/L, which is approximately double the baseline value. While this chlorine demand can be overcome by adding more chlorine, tests involving disruptions in aeration or feeding additional ammonia into the bioreactor produced much greater increases (>30x). The risks of increased chlorine demand on microbial safety can be overcome by limiting ammonia inputs to the system, providing backup systems to ensure sufficient aeration, or through additional anti-bacterial measures that do not depend on maintaining residual chlorine. [Display omitted] •Increasing loading up to 8x for 1 d produces manageable Cl2 demand.•Disrupted aeration produces high Cl2 demand from NH3 and DOC.•Increasing NH3 loading produces significant Cl2 demand due to NH3 passage.