Yeast supplementation alleviates the negative effects of greywater irrigation on lettuce and maize

Water scarcity has led to increased use of wastewater, particularly greywater, for crop irrigation. This study investigated whether the addition of yeast can alleviate the potential negative effects of greywater use on lettuce (Lactuca sativa L.) and maize (Zea mays L.). Seeds and seedlings were treated with 4 concentrations (0.005; 0.01; 0.015 and 0.020 g‧mL−1) of yeast-treated tapwater (YTW) and greywater (YGW). Tapwater (TW) and greywater (GW) without yeast served as controls. In general, an increase in yeast concentration compromised seed germination in Petri dishes, but improved germination in soil. Tapwater was more effective than GW in promoting germination and growth in both species. Lower concentrations of yeast generally increased germination capacity in both species compared to the controls. Total biomass, number of leaves, chlorophyll content, leaf area, photosynthetic rate and maximum quantum yield of photosystem II (Fv/Fm) were significantly higher in yeast treatments in both species, compared with the controls. Biomass accumulation, total leaf area, chlorophyll content and photosynthesis were higher in YGW than controls and YTW. Differences in biomass allocation between treatments may be due to changes in soil moisture, pH and electrical conductivity of the soil caused by yeast supplementation. This study showed that plants treated with YGW performed better than those treated with YTW and without yeast. Yeast supplementation of greywater could increase water recycling and provide a cheap bio-fertilizer to home growers, whilst significantly improving yield in both species. This innovative approach may enhance water and food security of subsistence farmers in rural areas.