Performance of pond–wetland complexes as a preliminary processor of drinking water sources

Abstract

Shijiuyang Constructed Wetland (110 hm2) is a drinking water source treatment wetland with primary structural units of ponds and plant-bed/ditch systems. The wetland can process about 250,000 tonnes of source water in the Xincheng River every day and supplies raw water for Shijiuyang Drinking Water Plant. Daily data for 28 months indicated that the major water quality indexes of source water had been improved by one grade. The percentage increase for dissolved oxygen and the removal rates of ammonia nitrogen, iron and manganese were 73.63%, 38.86%, 35.64%, and 22.14% respectively. The treatment performance weight of ponds and plant-bed/ditch systems was roughly equal but they treated different pollutants preferentially. Most water quality indexes had better treatment efficacy with increasing temperature and inlet concentrations. These results revealed that the pond-wetland complexes exhibited strong buffering capacity for source water quality improvement. The treatment cost of Shijiuyang Drinking Water Plant was reduced by about 30.3%. Regional rainfall significantly determined the external river water levels and adversely deteriorated the inlet water quality, thus suggesting that the "hidden" diffuse pollution in the multitudinous stream branches as well as their catchments should be the controlling emphases for river source water protection in the future. The combination of pond and plant-bed/ditch systems provides a successful paradigm for drinking water source pretreatment. Three other drinking water source treatment wetlands with ponds and plant-bed/ditch systems are in operation or construction in the stream networks of the Yangtze River Delta and more people will be benefited.

A Constructed Wetland System for Rural Household Sewage Treatment in Subtropical Regions

“…(1) The tested constructed wetland system was effective to remove TSS, COD Cr and BOD 5 , and the effluent concentrations of these three pollutants met the legislated discharge standards throughout the operation period. The average total removal rates determined in the tested period for TSS, COD Cr , BOD 5 , TN, NH 3 -N and TP were 85.3%, 82.4%, 80.1%, 47.5%, 51.0% and 61.8%, respectively.…”

“…The R a value of BIII represents the total removal rate R T of the system. Despite the great variation in pollutant loadings in the operation period, the designed system was very effective in the removal of TSS, COD Cr and BOD 5 . The observed concentrations of TSS, COD Cr and BOD 5 in the effluent of the final cell (BIII) met the first grade B of the legislated discharge standards (GB 18918-2002) throughout the tested year.…”

“…Despite the sharp increase in initial pollutant loadings in the cold period, the concentration of COD Cr (as well as BOD 5 and TSS) in the effluent of BIII remained below the GB1 (the stricter first B discharge standard) line throughout the operation period (Figure 2a). In comparison, the negative impact of the pollutant loadings on the removal of TN (Figure 2b), NH 3 -N ( Figure 2c) and TP (Figure 2d) was apparently exaggerated by the low temperature in the cold period, which raised the effluent concentrations of these three pollutants to significantly higher levels than their discharge standards.…”

“…Accounted for by its low construction and operation costs and ecologically responsible nature, constructed wetland technology (CW technology) has been rapidly developed as one of the alternative solutions for treatment of various types of wastewaters in different countries [1][2][3][4][5][6][7]. Examples [8,9] have shown that CW technology is very useful in rural and particularly mountainous areas where establishment of a centralized conventional treatment plant connected to long distance wastewater collection and transportation pipeline systems becomes an impossible option.…”

“…In order to obtain a better understanding of pollutant removal mechanisms, studies have been carried out by different workers on factors that determine the treatment efficiency of constructed wetland systems, including wetland types and combinations [5,10]; hydraulic and pollutant loads [2,11]; plant species [12][13][14]; substrates [15,16]; and their interactions [17,18], etc. The increasing trend in CW technology application coupled with stricter water quality standards requires development of better process design tools.…”