Recent insights into greywater treatment: a comprehensive review on characteristics, treatment technologies, and pollutant removal mechanisms

Engineered alginate-polyethyleneimine and sludge-aluminosilicate biochar composites for greywater treatment: Performance evaluation and models for designing pilot-scale systems

Greywater, originating from kitchen sinks and toilets, constitutes 75-80 % of the domestic wastewater produced in homes and can be reclaimed for non-potable uses. This study synthesized novel sludge-derived aluminosilicates and alginate-polyethyleneimine (PEI) biochar composites. The aluminosilicates offer a sustainable approach to sludge management, while alginate-polyethyleneimine presents a green biochar modification approach. Their performance in fixed bed columns for treating greywater was compared with zinc chloride, calcium alginate, and PEI-biochar composites. The CatBoost machine learning algorithm also predicted contaminant removal efficiency and breakthrough parameters. The morphological and chemical analyses showed that the modification techniques improved the physiochemical properties of the biochar, which in turn influenced contaminant removal efficiency. With its enhanced surface area and pore structure, zinc chloride-biochar demonstrated notable effectiveness in removing organic matter (highest COD removal efficiency 96.1 %). PEI-biochar exhibited a high removal efficiency for nitrates (highest value of 95.5 %), attributed to the positive amine groups. Aluminosilicate-biochar was the most effective at removing ammonium due to its high cation exchange capacity. The CatBoost algorithm successfully stimulated E. coli, total nitrogen, COD removal efficiencies, and breakthrough parameters from greywater using biochar (R2 > 0.7). Future research should conduct a pilot-scale study for this technology, explore the use of modified biochar arranged in multilayers for treating greywater, use of biochar for removing emerging contaminants in greywater, and optimize predictive models for greywater treatment. The insights from our study provide valuable guidance for effective and sustainable greywater treatment.

Technical implications of light greywater production and quality for decentralized treatment and reuse: A case study in Bucaramanga, Colombia

Decentralized light greywater (LGW) treatment and reuse can help mitigate urban water scarcity, yet data on its characteristics at the household level in Latin America remain scarce, limiting system design and implementation. This study assessed LGW quantity and quality in a representative household in Bucaramanga, Colombia, and analyzed its implications for decentralized treatment and reuse. Potable water consumption and LGW production from showers and hand basins were monitored over 98 and 124 days, respectively, with 27 LGW samples collected for quality analysis. Results showed that LGW production was 33.83 ± 4.10 (L/person)/day, accounting for 21% of household potable water consumption, with no significant differences across days of the week. Showers contributed 94% of LGW, while hand basins accounted for 6%. The volume of LGW was sufficient to meet toilet flushing demands (10% of potable water consumption) and could also support other accepted uses, such as floor cleaning and garden irrigation. LGW quality exhibited high variability, low nutrient content (6.37 ± 1.84 mgN/L and 0.74 ± 0.33 mgP/L), high organic matter concentrations (COD: 879.68 ± 163.51 mg/L; BOD5: 387.92 ± 92.08 mg/L), and fluctuating fecal coliform levels (1.87 × 105 ± 4.03 × 105 CFU/100 mL), influenced by personal care product use and hygiene practices. Effective treatment systems must accommodate water quality fluctuations and incorporate processes to remove suspended solids, turbidity, dissolved organic matter, oil and grease, and pathogens. This study identified three key technical implications of LGW production and quality for household-level treatment and reuse systems in decentralized settings.

Treated greywater as a novel water resource: The perspective of greywater treatment for reuse from a bibliometric analysis

The current global water crisis has prompted research into technologies that can reuse different water resources to mitigate water scarcity. The use of treated greywater can be proposed to provide additional water resources. By reusing this water in different applications, this water crisis can be mitigated at the local scale. This study presents a bibliometric analysis to assess the state of the art of greywater treatment and its reuse technologies. This analysis is based on the scientific literature published until 2023 in Scopus regarding greywater treatment and 1,024 documents were found. The results showed a clear exponential increase in the accumulated number of publications in this topic, which was spurred during the mid-1990s. The most prolific country was the United States, while China, the other typical scientific superpower in most fields, occupied the sixth position in the ranking. Environmental Sciences was the knowledge subject with more documents, followed by Engineering and Chemical Engineering. The bibliometric study was complemented using SciMAT to create bibliometric networks that represent the dynamic evolution of the themes. The most important themes were identified, among which three key points stand out: greywater characterization, technologies for greywater treatment, and water management, including the reuse of treated greywater.

Exploring biochar and Moringa oleifera seed proteins for greywater remediation on small farms

This study investigated the potential of using biochar and Moringa oleifera seed proteins for sustainable greywater treatment in rural Kenya. Greywater samples from washing clothes were collected from households in the Kenyan counties of Kwale and Siaya. Two treatment methods, batch stirring and filtration, were used to assess the effectiveness of using biochar and Moringa oleifera seed protein extract together to treat greywater at a household level. Both methods achieved a significant reduction in contaminants: colour was reduced by up to 43% in Kwale and 67% in Siaya, turbidity decreased by 91-98%, and surfactant levels were lowered by 89-93%. There were increases in total organic carbon and total dissolved solids post-treatment, but both methods effectively reduced levels of phosphates, nitrates and iron. This research highlights the potential of using locally available materials for greywater treatment and provides insights into sustainable water management nature-based solutions in the Global South.

Bacterial Contamination in the Different Parts of Household Washing Machine: New Insights from Chengdu, Western China

The moist and warm environment in the household washing machine provides ideal living conditions for the growth and survival of various microorganisms. However, the biodiversity of bacterial community in the different parts of washing machine from Chinese households has not been clarified. In this study, we assessed the bacterial communities in sealing strip, detergent drawer, inner drum, water filter and greywater of ten domestic washing machines quantitatively and qualitatively in Chengdu, southwestern China. The microbial cultivation results indicated that the washing machines from Chengdu had a severe microbial contamination reflected by large counts on bacteria, fungi and coliform. Furthermore, the sequencing data showed that the different parts displayed distinctive bacterial compositions. At the level of genus, the anaerobic bacteria of Caproiciproducens and Acidipropionibacterium were predominant in sealing strip. Barnesiella, Shinella and Sellimonas were detected as the characteristic bacteria in detergent drawer. The pathogens of Luteibacter and Corynebacterium at the genus level were the dominant bacteria in inner drum and water filter, respectively. The genera of Azospira, Roseococcus, Elstera and Aquicella, which belonged to the pathogenic phylum of Proteobacteria, were identified as bioindicators for the greywater. Gene function analysis on the sequencing data illustrated that the bacteria from washing machines were potentially associated with bacterial infectious diseases and antimicrobial resistance. This study shows the bacterial diversity in the different parts of washing machines, providing new clues for bacterial contamination in washing machines from Chinese households.

Eliminating xenobiotics organic compounds from greywater through green synthetic nanoparticles

Xenobiotic Organic Compounds (XOCs) have been widely considered to be pollutant compounds due to their harmful impacts on aquatic life. However, there have been few rigorous studies of cutting-edge technology used to eradicate XOCs and their presence in bathroom greywater. The present review provides a comprehensive examination of current methodologies used for removing XOCs by photocatalysis of green nanoparticles. It was appeared that zinc oxide nanoparticles (ZnO NPs) have high efficiency (99%) in photocatalysis process. Green synthesis provides proven processes that do not require dangerous chemicals or expensive equipment, making photocatalysis a potential solution for the status quo. XOCs residue was decomposed, and pollutants were eliminated with varied degrees of efficiency using green synthesis ZnO nanoparticles. It is hypothesized that the utilization of photocatalysis can create a greywater treatment system capable of degrading the toxic XOCs in greywater while increasing the pace of production. Hence, this review will be beneficial in improving greywater quality and photocatalysis using green nanoparticles can be an immediate platform in solving the issue regarding the existence of XOCs in greywater in Malaysia. Researchers in the future may benefit from focusing on optimizing photocatalytic degradation using green-synthesis ZnO. It might also help with the creativity and productivity of the next generation of authoritative concerns, notably water conservation.

Reduction of pathogens in greywater with biological and sustainable treatments selected through a multicriteria approach

Non-potable reuse of greywater (GW) can represent a valid alternative to freshwater consumption, satisfying the Sustainable Development Goals promoted by United Nations. The Multi-Criteria Analysis (MCA) was applied to select the most suitable processes for the reduction of microbiological contamination in GW. A pilot plant, including horizontal flow constructed wetland (CW) and anaerobic filtration (AF) in parallel, best treatment options according to MCA results, was built to treat GW collected from a Venezuelan family. (i) The removal efficiency of microbiological parameters, and (ii) the turbidity as possible microbiological contamination indicator and possible influence factor of disinfection treatment, were investigated. Except for Escherichia coli (4.1 ± 0.9 log reduction with AF), CW achieved the best reductions yields for total coliforms, faecal coliforms, and Salmonella, respectively equal to 3.1 ± 0.5 log, 4.3 ± 0.5 log, and 2.9 ± 0.4 log. In accordance with Venezuelan legislation and WHO guidelines, GW treated with CW was found to be suitable for irrigation reuse for non-edible crops. However, the reduction of pathogens by CW should be considered as a preliminary and not complete disinfection treatment. To reuse GW, especially in the irrigation of edible crops, stronger disinfection treatment should be considered as a complement to the preliminary disinfection performed by CW, to avoid any kind of risk. No significant correlation was found for turbidity either as a possible predictor of microbiological contamination or as an influence on biological disinfection.