The effect of tertiary treated wastewater on fish growth and health: Laboratory-scale experiment with Poecilia reticulata (guppy)

Assessing groundwater recharge rates, water quality changes, and agricultural impacts of large-scale water recycling

The over-exploitation and insufficient replenishment of groundwater (GW) have resulted in a pressing need to conserve freshwater and reuse of treated wastewater. To address this issue, the Government of Karnataka launched a large-scale recycling (440 million liters/day) scheme to indirectly recharge GW using secondary treated municipal wastewater (STW) in drought-prone areas of Kolar district in southern India. This recycling employs soil aquifer treatment (SAT) technology, which involves filling surface run-off tanks with STW that intentionally infiltrate and recharge aquifers. This study quantifies the impact of STW recycling on GW recharge rates, levels, and quality in the crystalline aquifers of peninsular India. The study area is characterized by hard rock aquifers with fractured gneiss, granites, schists, and highly fractured weathered rocks. The agricultural impacts of the improved GW table are also quantified by comparing areas receiving STW to those not receiving it, and changes before and after STW recycling were measured. The AMBHAS_1D model was used to estimate the recharge rates and showed a tenfold increase in daily recharge rates, resulting in a significant increase in the GW levels. The results indicate that the surface water in the rejuvenated tanks meets the country's stringent water discharge standards for STW. The GW levels of the studied boreholes increased by 58-73 %, and the GW quality improved significantly, turning hard water into soft water. Land use land cover studies confirmed an increase in the number of water bodies, trees, and cultivated land. The availability of GW significantly improved agricultural productivity (11-42 %), milk productivity (33 %), and fish productivity (341 %). The study's outcomes are expected to serve as a role model for the rest of Indian metro cities and demonstrate the potential of reusing STW to achieve a circular economy and a water-resilient system.

Socio-economic impact assessment of large-scale recycling of treated municipal wastewater for indirect groundwater recharge

Reusing treated wastewater is an emerging solution to address freshwater scarcity, and surface water contamination faced worldwide. A unique large-scale wastewater recycling project was implemented to replenish groundwater by filling secondary treated wastewater (STW) into existing irrigation tanks in severely drought-hit areas of the Kolar districts of Southern India. This study quantifies the socio-economic impacts of this large-scale indirect groundwater recharge scheme. The changes in areas receiving STW i.e., impacted areas and those areas which did not receive STW i.e., non-impacted areas was studied. Also, pre and post recycling changes were quantified in the Kolar district. The results show that surface water quality meets India's most stringent treated wastewater discharge standards prescribed by the Hon'ble National Green Tribunal. Due to these recycling efforts, significant improvements in groundwater level and quality were found. It was observed that there was a noticeable difference in agricultural cropping areas, seasons, patterns, and production between impacted and non-impacted areas. Post-recycling, farmers tended to cultivate cash and water-intensive crops over less water-intensive crops. During the post-recycling period, livestock and milk production also increased, and in impacted areas, it was significantly higher. Post-recycling, fish production increased and land prices per hectare increased by 118 % in impacted areas. The farmer's net income under flowers and vegetable farming increased by 202 % and 150 % respectively in impacted areas compared to non-impacted areas. Furthermore, this project contributes to a circular economy transition in the water sector, which has economic, environmental, social, and cultural benefits. A key recommendation from the outcomes of the study is to draft and implement a policy that encourages the reuse of recycled water for groundwater recharge which in turn will improve the agro-economic system and food security.

Integrated response of growth, antioxidant defense and isotopic composition to microplastics in juvenile guppy (Poecilia reticulata)

Microplastics (MPs) pollution becomes a research hotspot and many studies focus on threats of MPs, but few have integrated multi-level indicators to assess response to MPs of organisms. Here we exposed guppy (Poecilia reticulata) to MPs (polystyrene; 32-40 μm diameter) with two concentrations (100 and 1000 μg/L) for 28 days. We found that higher accumulation of MPs appeared in guppy gill than that in gut. MPs had no obvious effect on guppy growth but significantly inhibited the condition factor. Oxidative stress presented in guppy viscera with activated antioxidants. The decline of Na⁺/K⁺-ATP activity in guppy indicated that MPs might interfere with the osmotic balance of gills. MPs reduced body molar ratio of C:N and δ¹³C value, but no apparent impact on δ¹⁵N. It implied that MPs probably altered elemental transition. Eventually, through integrated biomarkers response index (IBR) of guppy, we found that catalase activity was the highest index in response to MPs, and the response of growth performance to MPs was lower than that of oxidative stress and element alteration. Risks of MPs aggravated in a concentration-dependent manner. These findings suggested that multi-level IBR approach should be adopted to quantify effects of MPs on aquatic organisms, especially on fish.

Exposure to microplastics impairs digestive performance, stimulates immune response and induces microbiota dysbiosis in the gut of juvenile guppy (Poecilia reticulata)

Microplastics (MPs) are widely distributing in aquatic environment. They are easily ingested by aquatic organisms and accumulate in digestive tract especially of intestine. To explore the potential effects of MPs on intestine, here we, using juvenile guppy (Poecilia reticulata) as experimental animal, investigated the response characteristics of digestion, immunity and gut microbiota. After exposure to 100 and 1000 μg/L concentrations of MPs (polystyrene; 32-40 μm diameters) for 28 days, we observed that MPs could exist in guppy gut and induce enlargement of goblet cells. Activities of digestive enzymes (trypsin, chymotrypsin, amylase and lipase) in guppy gut generally reduced. MPs stimulated the expression of immune cytokines (TNF-α, IFN-γ, TLR4 and IL-6). Through high throughput sequencing of 16S rRNA gene, decreases in diversity and evenness and changed composition of microbiota were found in guppy gut. PICRUSt analysis revealed that MPs might have effects on intestinal microbiota functions, such as inhibition of metabolism and repair pathway. Our findings suggested that MPs could retain in the gut of juvenile guppy, impair digestive performance, stimulate immune response and induce microbiota dysbiosis in guppy gut. The results obtained here provide new insights into the potential risks of MPs to aquatic animals.