Constructed wetlands can play an active role in improving the water quality of urban rivers. In this study, a sequential series system of the floating-bed constructed wetland (FBCW), horizontal subsurface flow constructed wetland (HSFCW), and surface flow constructed wetland (SFCW) were constructed for the urban river treatment in the cold regions of North China, which gave full play to the combined advantages. In the Yitong River, the designed capacity and the hydraulic loading of the system was 100 m3/d and 0.10 m3/m2d, respectively. The hydraulic retention time was approximately 72 h. The monitoring results, from April to October in 2016, showed the multiple wetland ecosystem could effectively remove chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total nitrogen (TN), total phosphate (TP), and suspended solids (SS) at average removal rates of 74.79%, 80.90%, 71.12%, 78.44%, and 91.90%, respectively. The removal rate of SS in floating-bed wetland was the largest among all the indicators (80.24%), which could prevent the block of sub-surface flow wetland effectively. The sub-surface flow wetland could remove the NH4-N, TN, and TP effectively, and the contribution rates were 79.20%, 64.64%, and 81.71%, respectively. The surface flow wetland could further purify the TN and the removal rate of TN could reach 23%. The total investment of this ecological engineering was $12,000. The construction cost and the operation cost were $120 and $0.02 per ton of polluted water, which was about 1/3 to 1/5 and 1/6 to 1/3 of the conventional sewage treatment, respectively. The results of this study provide a technical demonstration of the restoration of polluted water in urban rivers in northern China.

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Water-retaining earth structures often experience cyclic hydraulic flow patterns, which are believed to alter the soil fabric. Gap-graded soils are identified to be internally unstable. These soils exhibit a change in their hydraulic conductivity when the critical hydraulic gradient is exceeded. The changes beyond the critical hydraulic gradient, however, are yet to be understood. This research study examines the unsteady nature of clogging and unclogging process in saturated gap-graded soils subjected to hydraulic pulses. A set of 60 min flow (suffusion) tests was conducted using a positive displacement pump to subject a cylindrical specimen to controlled hydraulic flow pulses. The global hydraulic gradient across the specimen was continuously monitored. The grain-size distribution of the soil was re-evaluated after the test. The hydraulic shear stresses induced by the flow pulses were estimated numerically and normalised over the maximum value. Similar trends of the hydraulic conductivity and the applied flow rates do not hold when the duration of the flow pulse is increased. A simple procedure based on statistical inference is proposed to visualise the temporal variation of the clogging and unclogging process subjected to the frequency and the phase shift parameters of the flow pulse.

Evaluation of the efficiency of aircraft liquid waste treatment has previously been conducted to prevent pollution of the environment. The current study aimed to provide a set of practical methods for efficient airport sanitary supervision. Aircraft liquid waste was collected at Longjia International Airport, Changchun from multiple flights. The efficiency of liquid waste treatment as well as the water quality of the wastewater processed via a second-stage wastewater facility were examined by measuring a number of physical, chemical, and biological indices. Our results indicated that treatment solely via resolvable sanitizing liquid was not sufficient. Although the contents of first-class pollutants all met the requirements of the standard criteria, the contents of a number of second-class pollutants did not satisfy these criteria. However, after further treatment via a second-stage wastewater facility installed at the airport, all indices reached second-grade requirements of the discharge standard. We suggest that daily inspection and quarantine indices at airports should include the suspension content, biological oxygen demands after 5 days, chemical oxygen demand total organic carbon content, amino nitrogen content, total phosphorous content, and the level of fecal coliforms.

Aquatic plants have attracted wide attention because of their low cost and high level of resource utilization. In order to study the effects of emergent and submerged plants on the purification of different concentrations of wastewater, two common aquatic plants found in Northeast China, Iris ensata Thunb. and Potamogeton malaianus Miq., were selected Under static conditions, nitrogen and phosphorus removal from simulated wastewater with different concentrations (high, medium and low) and lake samples of Nanhu Park, Changchun, Jilin Province, China, were studied. The results showed that the removal rate of total nitrogen (TN) in medium- and high-pollutant concentration water samples and total phosphorus (TP) in medium- and low-pollutant concentration water with I. ensata reached more than 75%. The removal rate of TN in the medium-pollutant concentration water with P. malaianus reached 71.4%, while the removal efficiency of TN and TP in the low-pollutant concentration water was higher than 80%. It is more advantageous to use plants to purify high-pollutant concentration water after further purification. The purification plants suitable for medium-pollutant concentration water are limited, but under low-pollutant concentration water conditions, there are more diverse options regarding the choice of wastewater purification plants. In the Nanhu lake samples, I. ensata had the highest removal rates of TN (80.38%), and TP (85.62%). This study shows that both I. ensata and P. malaianus can be used as aquatic plants to restore the water quality of urban lakes. A reasonable combination of different plants for addressing different pollutants is more beneficial to improve the purification effect. This research provides an important basis for the phytoremediation and treatment of urban domestic wastewater and urban surface water bodies in northern China.