Abstract
A key characteristic of decentralized greywater treatment and reuse is high variability in both nutrient concentrations and flow. This variability in flow leads to stagnant water in the system and causes short-term fluctuations in the effluent water quality. Automated monitoring tools provide data to understand the mechanisms underlying the dynamics and to adapt control strategies accordingly. We investigated the fluctuations in a building-scale greywater treatment system comprising a membrane bioreactor followed by a biological activated carbon filter. Short-term dynamics in the effluent of the biological activated carbon filter were monitored with automated flow cytometry and turbidity, and the impact of these fluctuations on various hygiene-relevant parameters in the reuse water was evaluated. Continuous biofilm detachment into the stagnant water in the biological activated carbon filter led to temporarily increased turbidity and cell concentrations in the effluent after periods of stagnation. The fluctuations in cell concentrations were consistent with a model assuming higher detachment rates during flow than during times with stagnant water. For this system, total cell concentration and turbidity were strongly correlated. We also showed that the observed increase in cell concentration was not related to either an increase of organic carbon concentration or the concentration of two opportunistic pathogens, P. aeruginosa and L. pneumophila. Our findings demonstrate that turbidity measurements are sensitive to changes in the effluent water quality and can be used to monitor the fluctuations caused by intermittent flow. Intermittent flow did not lead to an increase in opportunistic pathogens, and this study provides no indications that stagnant water in biological activated carbon filters need be prevented.
Highlights
Greywater reuse for non-potable applications such as washing ma chines and showers must provide hygienically acceptable water at all times
Intermittent flow did not lead to an increase in opportunistic pathogens, and this study provides no indications that stagnant water in biological activated carbon filters need be prevented
When flow resumed after stagnation, both turbidity and total cell concentration (TCC) showed increased values in the biological activated carbon (BAC) effluent (Figure 2)
Summary
Greywater reuse for non-potable applications such as washing ma chines and showers must provide hygienically acceptable water at all times. This requirement renders the influence of short-term fluctuations in treated water quality important. An effective treat ment step in retaining bacterial pathogens is a membrane bioreactor (MBR) (Wu 2019) Opportunistic pathogens such as P. aeruginosa and L. pneumophila can grow after treatment due to remaining nutrients and nonsterile conditions and can cause serious hygienic problems for greywater reuse (Blanky et al 2017, Friedler et al 2011). The extent to which intermittent flow and biofilm detachment in the biofilter lead to a deterioration of hygiene-relevant parameters such as the con centration of opportunistic pathogens remains unclear
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