Reduction of pollution loads based on sewage treatment projects around a lake: A case study on Erhai Lake.

Erhai Lake is a highland freshwater lake in Dali, China. Rapid tourism development has generated large amounts of pollutants. Since 2015, six wastewater treatment plants (WWTPs) have been built to treat wastewater collected through sewage interception projects. In this study, reductions in the pollution load of wastewater from different sources were evaluated by considering the effects of groundwater leakage, microbial degradation, and rainfall-runoff. The results showed that the systems reduced the chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) loads by 85, 83, and 85%, respectively. Discharge wastewater has the characteristics of a low concentration of domestic sewage discharge, large tourist sewage discharge, and high concentration of livestock wastewater. Due to the high groundwater level, there is groundwater infiltration in the influent water of WWTPs, which dilutes the pollutant concentration of the influent and, therefore, results in a lower treatment efficiency. Further treatment of tailwater also reduced the pollution loads discharged into the lake as well as the COD and TN by 10.25 and 22.90%, respectively. The results indicate that groundwater infiltration in the sewer network system is the primary target to be addressed in future developments.

Seasonal and spatial distributions of euphotic zone and long-term variations in water transparency in a clear oligotrophic Lake Fuxian, China.

To assess the seasonal and spatial variations and long-term trends in water optical properties in Lake Fuxian, investigations based on field work in four seasons and a long-term analysis of data from 1980 to 2014 were conducted. The results show that there was no significant variation in the euphotic depth (Zeu) across the four seasons, and no significant correlations between Zeu and potential influencing factors in seasons other than summer, suggesting that the water itself may be a major factor regulating the Zeu in general. Nevertheless, significant differences in Zeu between the north region (NR) and the south region (SR) were observed in all seasonal tests except spring. This finding relates to a higher abundance of chromophoric dissolved organic matter (CDOM) in the NR due to runoff, especially in the rainy seasons (summer and autumn). CDOM and its terrigenous component had an important impact on Zeu in summer, with the highest precipitation, and impacts from suspended solids and non-algal particles were also found in the NR in summer. The Secchi disk depth in the lake decreased clearly over the years, with significantly negative correlations with the increasing permanganate index and air temperature, implying that organic contaminants (CDOM and/or phytoplankton) are important regulators of water transparency. We estimate that the combined effects of climate warming and changes in land use and land cover are also indirect regulating factors. These findings should be considered in the protection of Lake Fuxian, owing to the importance of light penetration in aquatic ecosystems.

Simulation and engineering demonstration of the advanced treatment of rainy overflow wastewater using a combined system of storage tank-wastewater treatment plant-wetland.

We propose a new technology to advanced treat overflow wastewater from a combined sewer system using a storage tank-wastewater treatment plant (STP)-constructed wetland (CW) system. The engineering demonstration (a 7,500 m3 storage tank and a 3,436 m2 CW) has been built to treat the combined sewer overflows (CSOs) at the largest combined rainwater/wastewater overflow outlet in the middle reaches of the Xinbaoxiang River, which is the second largest river in the Dianchi Lake Basin. During the rainfall period, CSOs enter the storage tank. After sedimentation purification, the higher concentration CSOs at the bottom enter the STP, and the upper low-concentration CSOs enter CWs, thereby linking the multiple means of treating CSOs and minimizing the impact of CSOs on the STP. During the dry season, CWs can also assist in purification of polluted river water. The supernatant (COD <80 mg/L) and the bottom part water (COD >200 mg/L) of the storage tank were sent to CWs and STP, respectively, for treatment. The project was stably operated over 6 months. The final effluent qualities were 12, 1.79, and 0.18 mg/L for COD, TN, and TP, respectively, which achieved the surface water class V standard. PRACTITIONER POINTS: A combined system of storage tank-wastewater treatment plant-wetland was proposed to advanced treat overflow wastewater of rainy season. The SWMM could calculate the water quality and volume of overflow under different rainfall conditions in the runoff area. The effluent of the engineering demonstration reached the standard of surface water class V.

Total phosphorus removal from domestic wastewater with Cyperus alternifolius in vertical-flow constructed wetlands at the microcosm level.

Vertical-flow constructed wetland (VFCW) is an effective alternative for removal of nutrients, heavy metals, and organic pollutants from wastewaters. This study investigated the uptake and removal of total phosphorus (TP) by Cyperus alternifolius from domestic wastewaters in the simulated VFCWs, The total of eight simulated VFCW treatments, including two different substrates, two different wet-to-dry ratios, and with and without C. alternifolius species (2 x 2 x 2 = 8), were utilized for an operation period of two years in this study. Results show that about 1.1 to 1.4 times more TP was removed from the influent with the presence of C. alternifolius as compared to without this plant species. A linear correlation existed between the aboveground biomass and its TP content. An increase in total biomass by 1000 g would result in an increase in TP accumulation in the aboveground biomass by 4.9 g. Large amounts of TP were removed by the substrate adsorption as compared to those by the aboveground biomass. Results suggest that, although substrate adsorption played a major role in TP removal, C. alternifolius uptake was an alternative pathway for further removal of TP from wastewaters in the VFCWs.