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Transformation of ammonium to nitrate upon sewage discharge to sub-surface environment exposes about 65 million households in rural and urban India to risks of drinking nitrate contaminated groundwater. Building on earlier research, a twin pit is modified in Mulbagal town, Karnataka, to remove nitrate in pit toilet sewage and is functional for nearly one year. The first pit serves as an anaerobic chamber, while the second pit facilitates aerobic reactions in the upper half and is equipped with a bio-barrier in its lower half. Quality of treated sewage is monitored by soil water samplers installed adjacent to the pit. After anaerobic digestion in pit 1, sewage flows into the aerobic chamber (upper half of pit 2), where COD/N ratio of 1.49 to 1.73 facilitates aerobic conversion of ammonium to nitrite and nitrate ions. Annamox reactions in a bio-barrier chamber (lower half of pit 2) reduce ammonium and nitrite concentrations, while denitrification reactions in the bio-barrier remove nitrite and nitrate from pit toilet sewage. Besides nitrate, the modified twin pit reduces COD (chemical oxygen demand), ammonium, and thermotolerant coliform levels in the discharged sewage.

Anthropogenic activities impact the major ion composition of fresh water sources. The inorganic species are likely to be influenced by mineral dissolution, mineral precipitation, redox and ion-exchange reactions in the contaminated lakes. Owing to paucity of research, this study examines the influence of bio-geochemical reactions on the major ion composition of sewage contaminated Bengaluru lakes. The selected lakes represent water bodies in the major valley systems of the city that are polluted by partly treated sewage and stormwater runoffs. Hydrogeochemical facies of the lake samples showed that enrichment of Mg 2+ , Na + , Cl − and SO 4 2− ions from anthropogenic contamination altered the chemical type of the lake-water. Examination of processes influencing the major ion composition of surface waters indicated that evaporation than rock-weathering tends to influence the chemical composition of the Bengaluru lakes. Precipitation of carbonate minerals in the alkaline pH contributed to the deficiency of alkaline earth ions, while dissolution of anthropogenic gypsum enhanced the SO 4 2− ion concentration of the lakes. Solute diffusion from lake water into the pore solutions of sediments and ion-exchange reactions between monovalent ions of sediments and divalent cations in lake water are additional pathways that influence the major ion composition of the contaminated lakes. Besides alterations in major ion composition, organic contamination, biochemical reactions associated with photosynthesis activity of algae and release of toxic Al 3+ ions from mineral dissolution are consequences of the lake contamination.

This study utilised native denitrifiers of cattle manure to oxidise its organic matter and induce calcium carbonate cementation in a synthetic soft soil. The soft soil is prepared by remoulding a 50% kaolinite + 50% sand mix with ultra-pure water at 21% water content. The prepared specimen is classified as soft soil based on its low unconfined compression strength of 16 kPa. Extraneous calcium nitrate provides nitrate ions (electron acceptors) for the metabolism of denitrifying bacteria and calcium (Ca2+) ions for calcium carbonate formation. The facultative anaerobe community peaks and declines between 7 and 14 days. A small addition of magnesium oxide balances the pH reduction caused by acetic acid formation during microbial degradation of cattle manure. Acetic acid serves as a carbon substrate for the metabolic activities of denitrifying bacteria. The CO2 (gas) released during the metabolic activities of bacteria dissolves in water and forms bicarbonate ions. The anion combines with calcium ions in the alkaline environment to form calcium carbonate cement. In addition, the native extracellular polysaccharide (EPS)-secreting bacteria in cattle manure facilitate EPS bonding of soil aggregates. Soil structure, interfacial frictional resistance mobilised by cattle manure fibres, EPS bonding and calcium carbonate cementation enhance the compression strength of the stabilised specimen by 720%.

Monitoring water quality to minimize deterioration of a lake’s functionality is important, as several Indian lakes are exposed to sewage contamination. Public health laboratories, citizen scientists, and volunteers in developing nations often find it difficult to perform elaborate tests to monitor the water quality of freshwater systems. Developing a classification method to evaluate the pollution status of sewage-contaminated lakes using limited tests will expand environmental monitoring of freshwater systems and contribute valuable data to the regional and global repository. Four classes of lake pollution ranging from unpolluted (class 1) to mixed wastewater (class 4) were identified based on the distribution of data points in the K+ (potassium) versus COD (chemical oxygen demand) scatter chart. As pH, EC (electrical conductivity), turbidity, and DO (dissolved oxygen) are deteriorated by sewage contamination, these parameters were also incorporated in the proposed pollution classification table. Data of unpolluted and sewage polluted Indian lakes were employed to compile the limiting range of parameters in the proposed lake pollution classification. The five parameters (K+, pH, EC, DO, turbidity) required to categorize lake pollution (class 1 to 4) can be measured with equipment costing 800–1000 USD, while COD can be measured at 5 USD/sample in laboratories.

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The study examines the impact of evaporation on the fate of ammonium-N reactions in blackwater-contaminated soils. During evaporation, ammonia (g) volatilization is the preferred route of NH4-N transformation and nitrate formation is initiated thereafter. Ammonia volatilization ceased at residual blackwater contents of 16–40% owing to loss of air-void connectivity. Experimental results indicated that owing to ammonia volatilization and reduced blackwater content only 23–35% of initial NH4-N concentration was transformed to NO3-N. This study also predicted the nitrate accumulation in Mulbagal town aquifer due to blackwater discharge from pit toilets. The prediction indicated that the permissible (45 mg/L) nitrate concentration in the aquifer may have been breached several decades ago, exposing the populace to prolonged drinking water contamination.