Arsenic pollution and its treatment in Yangzonghai lake in China: In situ remediation

In this study, the effect of direct atomization and spraying a ferric chloride (FeCl3) solution to decrease the arsenic concentration and its pollution in Yangzonghai Lake, China, was investigated. Ten ships were used for spraying 6–8t of FeCl3 in the lake every day since October 2009. After spraying, the average concentration of arsenic in Yangzonghai Lake, which has an area of 31km2, an average depth of 20m, and a water storage capacity of 604 million m3, started to decrease from 0.117mgL−1. On 20 September 2010, the lowest arsenic level of 0.021mgL−1 was attained, with an arsenic removal rate as high as 82.0%. However, the source of pollution was not eliminated, and local rainfall mainly occurred in September; hence, arsenic concentration from October to December increased to 0.078mgL−1. At the beginning of 2011, the As concentration decreased and remained at 0.025–0.028mgL−1 from May to September. During the 2 years of FeCl3 treatment, the water quality improved from V Class to II–III Class of the Chinese standards, which remained consistent for 12 months. The total cost for this in situ water treatment was 29 million RMB, which was less than a hundredth of the expected expenditure of 4–7 billion RMB. The treatment method achieved goals such as high arsenic removal rate, easy operation, low cost, and ecological security. In this study, the changing patterns of the concentration of arsenic in Yangzonghai Lake from June 2008 to December 2014 were analyzed, and the following problems were discussed: the stability of iron-arsenic precipitates in the lake, the concentrations of ferric and chloride ions in the lake, the pH of the lake during treatment, the stability of iron-arsenic precipitates in the lakebed sediments, and the variation of phytoplankton species in the lake.