Treating agricultural non-point source pollutants using periphyton biofilms and biomass volarization.

Untreated domestic wastewater and agricultural runoff are emerging as a potent cause of non-point source (NPS) pollutants which are a major threat to aquatic ecosystems. Periphyton biofilm-based technologies due to their high growth rate, energy efficiency and low input costs offer promising solutions for controlling nutrient pollution in agricultural systems. In this study we employed periphyton floway to treat NPS pollution from the agricultural watershed. The process performance of outdoor single pass algae floway (AFW) was evaluated. Steady state average biomass concentration of 11.73 g m-2 d-1 and removal rate of nitrogen: 0.60 g m-2 d-1, phosphorus: 0.27 g m-2d-1, arsenic: 9.26 mg m-2 d-1, chromium: 255.3 mg m-2 d-1 and lead: 238.6 mg m-2 d-1 was achieved. In addition, the microalgae and their associated bacterial diversity and dynamics were analyzed. The results revealed a high diversity and rapid variations in the microbiome structure with diatom and cyanobacteria dominance combined with high N fixing and P solubilizing bacteria during most of the operational period. Elemental analysis of periphyton biomass was done for its safe use as slow-release fertilizer. Biofuel feedstock potential and nanoparticle generation potential of the biomass were analyzed. This work highlights the potential use of periphyton biofilms in remediation and recycling of NPS pollutants with simultaneous resource recovery.

Constructed wetland for improved wastewater management and increased water use efficiency in resource scarce SAT villages: a case study from Kothapally village, in India.

Evaluation a field-scale of constructed wetland (CW) for the treatment of rural wastewater (WW), in resource-scarce semi-arid tropic (SAT) villages, to provide improved wastewater management and increased water use efficiency, was the main objective of this study. A CW was commissioned in Kothapally village of Telangana to treat the wastewater generated from 100 households. The CW was vegetated with Typha latifolia and Canna indica. Average COD, sulfate and inorganic nitrogen removal efficiencies observed were 65%, 60% and 67% respectively, for the study period (one year). Removal efficiency for total coliform was consistently above 80%. The treated wastewater was stored in a farm pond and was utilized for irrigation in the nearby agricultural fields (0.6 ha). This perennial source of water, helped the nearby farmers to cultivate two additional crops, chickpea during rabi and sweetcorn during summer. The assured availability of water reduced their vulnerability to dry spells during the kharif by providing means for lifesaving irrigation. The biomass harvested from the constructed wetland was used as fodder for the livestock. A net additional income of Rs.70,000 (∼US$1,000) was realized by the farmers using the treated wastewater for cultivation. Similar constructed wetland-based wastewater management system can be scaled up across water scarce semi-arid tropics. Novelty statementField-scale performance evaluation of constructed wetland based wastewater treatment in a semi-arid tropic village is scarce in the literature. The work presented gives a feasibility assessment for this technology critical for its wide-scale application to augment rural wastewater management in resource poor villages.

Identifying potential zones for rainwater harvesting interventions for sustainable intensification in the semi-arid tropics.

Decentralized rainwater harvesting (RWH) is a promising approach to mitigate drought in the drylands. However, an insufficient understanding of its impact on hydrological processes has resulted in poor resource planning in this area. This study is a meta-analysis of 25 agricultural watersheds representing a range of rainfall and soil types in the semi-arid tropics. Rainfall-runoff-soil loss relationship was calculated at daily, monthly and yearly levels, and the impact of RWH interventions on surface runoff and soil loss was quantified. A linear relationship was observed between daily rainfall and surface runoff up to 120 mm of rainfall intensity, which subsequently saw an exponential increase. About 200-300 mm of cumulative rainfall is the threshold to initiate surface runoff in the Indian semi-arid tropics. Rainwater harvesting was effective in terms of enhancing groundwater availability (2.6-6.9 m), crop intensification (40-100%) and farmers' incomes (50-200%) in different benchmark watersheds. An average of 40 mm of surface runoff was harvested annually and it reduced soil loss by 70% (3 ton/ha/year compared to 1 ton/ha/year in non-intervention stage. The study further quantified runoff at 25th, 50th and 75th percentiles, and found that more than 70% of the area in the Indian semi-arid tropics has high to medium potential for implementing RWH interventions.

Impact of Rainwater Harvesting on Hydrological Processes in a Fragile Watershed of South Asia.

Agricultural water management (AWM) interventions play an important role in ensuring sustainable food production and mitigating climate risks. This study was carried out in a watershed located in a low rainfall (400-600 mm) region of western India. The Soil and Water Assessment Tool model was calibrated using surface runoff, soil loss, and reservoir storage levels, between the year 2000 and 2006. The investigation indicated that the various AWM interventions increased groundwater recharge from 30 mm/year to 80 mm/year and reduced surface runoff from 250 mm/year to 100 mm/year. The intervention structures were refilled two to three times during the monsoon season depending on rainfall intensity and duration. The interventions have the advantage of building a resilient system by enhancing groundwater availability even in dry years, stimulating crop intensification and protecting the landscape from severe erosion. The results indicate that soil erosion has been reduced by more than 75% compared to the nonintervention situation. Moreover, the AWM interventions led to the cultivation of 100-150 ha of fallow land with high-value crops (horticulture, vegetables, and fodder). Household income increased by several folds compared to the nonintervention situation. The study showed about 50% reduction in downstream water availability, which could be a major concern. However, there are a number of ecosystem trade-offs such as improved base flow to the stream and reduction in soil loss that should be considered. The study is of great importance to stakeholders to decide on the optimal design for AWM interventions to achieve sustainable development goals.

Wealth from waste: Diatoms as tools for phycoremediation of wastewater and for obtaining value from the biomass.

Diatoms are a type of microalgae with diverse capabilities which make them useful for multiple applications. The abundance of diatoms in water bodies facilitates the removal of pollutants from wastewater originating from different industries, such as agriculture and other anthropogenic sources. The unique photosynthetic, cellular and metabolic characteristics of diatoms allows them to utilize pollutants like nitrate, iron, phosphate, molybdenum, silica, and heavy metals, such as copper, cadmium, chromium, lead, etc., which make diatoms a good option for wastewater treatment. In addition, the biomass produced by diatoms growth on wastewaters has diverse applications and can, therefore, be valuable. This review focusses on the unique capabilities of diatoms for wastewater remediation and the capture of carbon dioxide, concomitant with the generation of valuable products. Diatom biorefinery can be a sustainable solution to wastewater management, and the biomass obtained from treatment can be turned into biofuels, biofertilizers, nutritional supplements for animal production, and used for pharmaceutical applications containing bioactive compounds like EPA, DHA and pigments such as fucoxanthin.

Biodiesel production through algal cultivation in urban wastewater using algal floway.

The aim of this work was to study algal floway (AFW) to treat urban wastewater and to evaluate biomass productivity, lipid contents and biodiesel production. The results indicated the seasonal average algae productivity of 34.83 g dry weight m2 d-1 with a nutrient removal rate of 2.52 g m2 d-1N and 1.25 g m2 d-1P while the lipid content ranged between 14 and 22% of dry cell weight with the highest lipid productivity of 9.29 g m-2 d-1 during summer. Biodiesel quality was superior during summer with high centane number and cold filter plugging point values. High eicosapentaenoic acid content was found during winter growth cycles. AFW algae community was dominated by pennate diatoms during all growing seasons. This study is one of its kinds in Indian wastewaters and it provides fundamental information for further optimization and use of AFW to treat domestic wastewater and to produce algae biofuel feedstock.