Chemical composition, nutrient-balancing and biological treatment of hand washing greywater

Abstract

On-site biological hand washing water treatment can improve global access to safe hand washing water, but requires a thorough understanding of the chemical composition of the water to be treated, and an effective treatment strategy. This study first presents a detailed characterization of the individual inputs to hand washing water. We demonstrate (i) that soap is likely the most significant input in hand washing water, representing ∼90% of mass loading, and (ii) that inputs to hand washing water have low concentrations of biologically-essential macro- and micro-nutrients (nitrogen, phosphorus, potassium, copper, zinc, molybdenum and cobalt) with respect to carbon, which may impair biological carbon removal. This study next formulates a recipe that recreates a representative composition of hand washing water and develops a procedure to identify and supplement nutrients in which this recipe is estimated to be deficient. Batch testing of the nutrient-supplemented hand washing water with an inoculum of planktonic bacteria demonstrated improved assimilable organic carbon removal (99% vs. 86% removal) and produced lower final dissolved organic carbon concentrations (1.7 mgC/L vs. 3.5 mgC/L) compared to realistic (nutrient-deficient) washing water. Supplementing nutrients did promote cell growth (50x higher final total cell count). Full-scale testing in a biologically activated membrane bioreactor (BAMBi) system treating 75 L/day of nutrient-supplemented hand washing water showed that long-term operation (100 days) can deliver effective carbon removal (95%) without detrimental fouling or other disruptions caused by cell growth. This work demonstrates that biological treatment in a BAMBi system, operated with appropriate nutrient-balancing offers an effective solution for decentralized treatment of light greywater.

Comparing the anti-bacterial performance of chlorination and electrolysis post-treatments in a hand washing water recycling system

“…Long-term testing with a BAMBi fed a mixture of feces, urine, soap and water has demonstrated 95% removal of organic carbon (Künzle et al., 2015) as well as stable nitrification and denitrification (Ravndal et al., 2015). Similar performance has been demonstrated treating a synthetic hand washing greywater (Ziemba et al., 2018). BAMBi utilizes a gravity-driven membrane (GDM) which requires no additional pressure to be applied to the feed side of the membrane beyond the weight of water.…”

“…The recipe for the synthetic feed was taken directly from, and is described in great detail by, Ziemba et al. (2018).…”

“…This study utilizes a previously developed water treatment system known as a biologically activated membrane bioreactor (BAMBi) (Künzle et al., 2015). Our primary reasons for selecting the BAMBi system are, (i) the simplicity, small footprint and the low-maintenance operation of the BAMBi make the system practical and affordable for lower-income communities (Künzle et al., 2015; Ravndal et al., 2015), (ii) long-term testing has demonstrated stable operation and effective contaminant removal from synthetic hand washing water (Ziemba et al., 2018). The core technology of the BAMBi is an ultrafiltration membrane submerged in a treatment tank.…”

Decentralized treatment and recycling of greywater from a school in rural India

“…A recent study had also reported that handwashing soap is the dominant ingredient in the handwash water [36]. In the handwash area the students were instructed not to use any soaps as that could potentially increase the nutrient level in the HW water.…”

Membrane processes

“…Photocatalytic ozonation reduced approximately 60% of total organic carbon (TOC) and 97% of bacterial content from graywater, while the combination with electro-MBR increased TOC removal to 80%. Ziemba et al (2018) studied the use of a household-scale biologically activated MBR (BAMBi) system to treat graywater for potential reuse. Supplemental nutrients were used to increase the reduction of organic carbon to 95%.…”