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

Abstract

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 Cl 2 /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.

Light or Dark Greywater for Water Reuse? Economic Assessment of On-Site Greywater Treatment Systems in Rural Areas

“…Water quality monitoring of treated greywater includes the costs of water analysis (C a ) and water samples transport (C t ), and is performed quarterly as required by current Chilean regulations. Disinfection costs consider the use of liquid chlorine (sodium hypochlorite 15%) as a disinfectant and the estimated cost is associated with the use of 0.014 kg/m 3 of treated greywater (US$1.54/kg sodium hypochlorite 15%) [29,30]. These costs were estimated according to our own data from the monitoring of light greywater treatment systems and the technical capabilities of the equipment used (theoretical and empirical).…”