Temporal Variation and Reduction Strategy of Nutrient Loads from an Urban River Catchment into a Eutrophic Lake, China

Evaluation of reduction of external load of total phosphorus and total suspended solids for rehabilitation of urban lakes

Urban lakes provide important services to cities, but they suffer from en-vironmental problems, mainly resulting from degradation of the watershed. Rehabilitation of degraded lakes is based on the recovery of water quality and reduction of external pollution, the latter usually taking priority. The Lagoa da Pampulha (LP) is an artificial lake located in Belo Horizonte, Minas Gerais - Brazil, that has suffered eutrophication and silting for decades and has been undergoing rehabilitation for some years. The objective of this study was to evaluate the importance of sanitary, environmental and urban improvements implemented in the LP watershed. For this purpose, total phosphorus (TP) and total suspended solid (TSS) loads transported to LP, between 2016 and 2017, obtained from hydrological and water quality monitoring data, were estimated. Additionally, simulations were carried out using the Storm Water Management Model (SWMM) to evaluate TP and TSS loads in hypothetical scenarios. The conservative scenario proposed a reduction of 50 % in sanitary sewage discharge to water courses and an increase of 30 % and 10 % in the urban area and non-vegetated soil, respectively, in the watershed. In an op-timistic scenario, a reduction of 95 % in sewage discharge and a reduction of 50 % in non-vegetated soils was proposed. According to the results obtained, between October 2016 and September 2017, about 38 tons of TP and 3000 tons of TSS were transported into LP. The results of the SWMM simulations indicated high loads entering the lake, ranging from about 23,000 to 13,000 ton/year for TP and from 3200 to 2400 ton/year for TSS, in actual and optimistic scenario respectively. Despite presenting significant reductions, of up to 60 % for TP and 25 % for TSS, the loads transported to LP remained high even in the most optimistic scenario, indicating that implementation of the evaluated improvements only not sufficient to guarantee rehabilitation of the lake, and must be associated with other measures.

Reed Biochar Addition to Composite Filler Enhances Nitrogen Removal from BDBR Systems in Eutrophic Rivers Channel

With the rapid development of urbanization in China, the eutrophication or black stink of urban rivers has become a critical environmental problem. As a research hotspot in wastewater purification, biofilm technology has shortcomings, such as insufficient carbon sources for denitrification. This study used a Biofilm Denitrification Batch Reactor (BDBR) system constructed using reed biochar as the carbon source required in denitrification, significantly accelerating the biofilm formation. To determine the suitable amount of biochar for water purification from the urban eutrophic rivers by the BDBR system, 0%, 5%, 10%, and 15% reed biochar was added to the viscose fiber combined packing. The combined packing reactor involved in this study had a high removal efficiency of the eutrophication channel COD throughout the experiment. However, adding 5% and 10% biochar in the combined filler effectively increased the number of nitrifying and denitrifying bacteria on the biofilm, improved the dominant bacteria diversity and microbial activity, and enhanced denitrification efficiency in the BDBR system. It provides new ideas and methods for developing and applying in situ denitrification technology for urban polluted rivers.