Greywater as an Alternative Solution for a Sustainable Management of Water Resources—A Review

Production of polyhydroxyalkanoates using sewage and cheese whey

Recently, polyhydroxyalkanoates (PHAs) have been produced using raw sewage in our laboratory; however, the production concentrations are low. Therefore, this study aimed to enhance PHA production by applying different strategies. PHA production was higher in sewage-containing medium than in mineral salt medium and was enhanced 22-fold after glucose supplementation. A relatively high degree of glucose consumption (83.6 ± 1.59 %) was also achieved. Bacteria incubated with cheese whey diluted with sewage showed higher PHA production than bacteria incubated with cheese whey diluted with distilled water did. The expression of the PHA synthase gene (phaC) was evaluated via real-time polymerase chain reaction using low- and high-carbon-containing sewage. Relatively higher phaC expression levels were observed in high-carbon-containing sewage but at lower nitrogen concentrations. The characteristics of the produced PHA were comparable to those of standard PHA. Therefore, this study revealed that the bacterium Bacillus sp. CYR1 can produce PHA from low- or high-carbon-containing wastewater.

Economics of household preferences for water-saving technologies in urban South Africa

Drought severity is expected to increase in South Africa in the coming years, given the deteriorating effects of climate change on rainfall patterns, global temperature, and evaporation. A common mitigation strategy adopted by households is to promote water demand management initiatives to reduce water consumption volume and complement existing water supply management approaches implemented by suppliers. This study contributes to the discussion on adaptation strategies by investigating household preference heterogeneity for water-saving technologies through empirical evidence from urban Cape Town, South Africa. Using a choice modelling framework, we collected primary survey data from 512 urban households in five of the city's major suburbs and investigated heterogeneity among the households based on their preferences for characteristics embedded in four water-saving technologies. Four preference classes were identified by accounting for taste heterogeneity. Overall, respondents had the highest marginal willingness to pay (MWTP) for the greywater technology alternative at 17,025 ZAR (US$ 1142) while rainwater technology has the least willingness to pay value at 5206 ZAR (US$ 349). In addition, the results show that respondents in classes 1 and 2 have a high interest in technologies that save a large quantity of water, whereas members of classes 3 and 4 rely on inexpensive conservation and behavioral habits as climate adaptation measures. This study has important policy implications for many water-stressed and arid cities within and outside South Africa since like Cape Town, many large cities require long-lasting measures that help reduce the pressure on their strained water systems.

Comparative analysis of greywater pollutant removal efficiency with horizontal free water surface flow wetland with other wetland technologies

The reuse of treated wastewater for agriculture and other purposes is globally recognized as a reliable water source. Constructed wetlands are cost-effective and reliable green technologies for wastewater treatment, offering an environmentally friendly and affordable solution with minimal operational and maintenance requirements. This study assessed four wetland technologies (HFWSF, VFSF, VSSF, and HSSF) for treating greywater according to regulatory standards. The technologies effectively maintained pH levels, and both treated and untreated greywater samples met FEPA limits. They efficiently reduced dissolved and suspended particles, remaining below FEPA discharge limits for conductivity, TDS, turbidity, and TSS. However, elevated ammonia levels in both treated and untreated samples required additional treatment or mitigation. Sulphate levels were successfully mitigated, and phosphorus limits were met, with HFWSF already compliant even before treatment. Nitrate levels were reduced to meet FEPA limits, ensuring regulatory compliance. While BOD limits were met in both treated and untreated samples, untreated samples exceeded COD limits, necessitating more efficient treatment methods. HFWSF and HSSF complied with COD limits, whereas VFSF and VSSF did not. Both treated and untreated samples exceeded FEPA limits for oil and grease, indicating the need for additional treatment. Untreated samples exhibited high coliform contamination levels, underscoring the importance of effective treatment. However, all technologies successfully reduced coliform levels in treated samples, meeting FEPA limits and confirming treatment effectiveness. The combination of Typha (Domingensis) in the horizontal subsurface flow constructed wetland improved pollutant removal, nutrient removal, and contaminant elimination. Incorporating water Hyacinth (Eichhornia crassipes) with horizontal free water surface flow wetland technology demonstrated the highest efficacy in removing various pollutants. This combination outperformed other wetland technologies in effectively removing pollutants, including ammonia (60%), oil and grease (78.46%), COD (85%), TP (37.04%), FC (75%), and TC (79.59%), representing significant progress in greywater treatment.