Membrane distillation of concentrated blackwater: Effect of temperature, solids concentration and membrane pore size

Abstract

This study has elucidated the mechanisms governing water recovery from blackwater using membrane distillation, and has clarified the role of the organic particle fraction on membrane performance. Whilst fecal pathogen growth was initially observed at lower temperatures, pathogen inactivation was demonstrated over time, due to urea hydrolysis which liberated ammonia in excess of its toxic threshold. During the growth phase, membrane pore size <0.45 µm was sufficient to achieve high log reduction values for Escherichia coli, due to size exclusion complimented by the liquid–vapor interface which enhances selective transport for water. Higher feed temperatures benefitted rejection by promoting thermal inactivation and suppressing urea hydrolysis. Whilst the mechanism is not yet clear, suppression of hydrolysis reduced bicarbonate formation kinetics stabilizing the ammonia‐ammonium equilibrium which improved ammonium rejection. Blackwater particle concentration was studied by increasing fecal content. Particle fouling improved selectivity for coarse pore membranes but increased mass transfer resistance which reduced flux. Particle fouling induced wetting as noted by an eventual breakthrough of feed into the permeate. We propose that by incorporating upstream solid–liquid separation for particle separation to limit wetting and mass transfer resistance, membrane distillation can be a reliable solution for the recovery of high‐quality permeate from blackwater. Practitioner points Membrane distillation demonstrated for concentrated blackwater. Multiple factors provide robust pathogen separation (pore size, vapor–liquid interface, temperature, free‐ammonia). Excellent water quality produced for feed 40 times more concentrated than wastewater. Removing particle fraction will improve separation robustness and operating longevity.

Downscaling reverse osmosis for single-household wastewater reuse: towards low-cost decentralised sanitation through a batch open-loop configuration

“…Average urine and faeces mass flows of 2.2 L person À1 day À1 and 0.026 kg person À1 day À1 , respectively were assumed (Rose et al 2015). The faeces mass flow was below that nominally assumed per capita (0.128 kg capita À1 day À1 Rose et al 2015) to account for upstream solid/liquid separation by the toilet interface, where 80% total suspended solids removal has been demonstrated with source separation (Kamranvand et al 2021). Tap water was used to simulate flush water comprising 2.7 L person À1 day À1 , equivalent to the flow rate from a low flush toilet.…”