The study reported and analyzed the current state of wastewater treatment plants (WWTPs) in urban China from the perspective of treatment technologies, pollutant removals, operating load and effluent discharge standards. By the end of 2013, 3508 WWTPs have been built in 31 provinces and cities in China with a total treatment capacity of 1.48×10(8)m(3)/d. The uneven population distribution between China's east and west regions has resulted in notably different economic development outcomes. The technologies mostly used in WWTPs are AAO and oxidation ditch, which account for over 50% of the existing WWTPs. According to statistics, the efficiencies of COD and NH3-N removal are good in 656 WWTPs in 70 cities. The overall average COD removal is over 88% with few regional differences. The average removal efficiency of NH3-N is up to 80%. Large differences exist between the operating loads applied in different WWTPs. The average operating loading rate is approximately 83%, and 52% of WWTPs operate at loadings of <80%, treating up to 40% of the wastewater generated. The implementation of discharge standards has been low. Approximately 28% of WWTPs that achieved the Grade I-A Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918-2002) were constructed after 2010. The sludge treatment and recycling rates are only 25%, and approximately 15% of wastewater is inefficiently treated. Approximately 60% of WWTPs have capacities of 1×10(4)m(3)/d-5×10(4)m(3)/d. Relatively high energy consumption is required for small-scale processing, and the utilization rate of recycled wastewater is low. The challenges of WWTPs are discussed with the aim of developing rational criteria and appropriate technologies for water recycling. Suggestions regarding potential technical and administrative measures are provided.

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The impact of hydraulic loading rate (HLR) and seasonal temperature on contaminant removal efficiencies within an integrated constructed wetland (ICW) system of 3.25 ha was assessed. The ICW system was designed to treat domestic wastewater from Glaslough (Ireland). The current loading rate is 800 population equivalents. The system has shown good removal performances (2008 to 2010). Mean concentration removal efficiencies were high: 92% for chemical oxygen demand (COD), 98% for the 5 days at 20°CN-allylthiourea biochemical oxygen demand (BOD), 94% for total suspended solids (TSS), 97% for ammonia-nitrogen (NH 3 -N), 90% for nitrate-nitrogen (NO 3 -N), 96% for total nitrogen (TN), and 96% for molybdate reactive phosphate (MRP). The mean mass removal efficiencies were 92% for COD, 98% for BOD, 96% for TSS, 92% for NH 3 -N, 83% for NO 3 -N, 90% for TN, and 91% for MRP. Loading rate fluctuations were mainly due to high variation in rainfall (0.4 to 400 m 3 day -1 ) and in evapotranspiration rate (0 to 262 m 3 day -1 ). The influence on the removal efficiencies of the hydraulic loading rate (−0.7 to 15.3 cm day -1 ), which was based on overall water balance, was negligible. This implies that the large footprint of the system provides a high hydraulic retention time (92 days).

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The characteristics of nitrogen (N) and phosphorus (P) removal were studied during the 2-year operation of a free water surface flow wetland of 900 m² with hydraulic loading of 0.1 m/d to evaluate its potential to treat water from an urban stream polluted with municipal and industrial wastewater. Attention was focused on the removal of dissolved N and P by harvesting plants (local Phragmites australis and Typha orientalis) at the end of each growing season. According to findings, the removals of N and P increased from 47.1% and 17.6%, respectively, in the 1st year to 52.3% and 32.4%, respectively, in the 2nd year. Increments of N and P removal were largely attributable to plant biomass, which increased from an average dry weight of 1.77 kg/m² in the 1st year to 3.41 kg/m² in the 2nd year. The amount of nutrients assimilated by plants in the 2nd year was almost double that of the 1st year. Increasing biomass in the 2nd year also improved redox conditions in the substrate layer, which contributed to increasing the efficiency of N removal. Compared with T. orientalis, P. australis was more competitive and adapted to conditions in the wetland better; it regenerated more vigorously and contributed more to nutrient removal.