Optimizing structure and operation of rapid artificial filtering system for high-intensity farmland drainages

Abstract

【Objective】 The rapid artificial filtering system (CRI) is a technology to purify drainage water from farmland. In this paper, we examine the efficiency of CRI with different filler combinations to purify drainage water characterized by high-intensity drainage rate and low pollutant concentrations. 【Method】 The experiments consisted of five pollutant loads represented by different nitrogen and phosphorus concentrations and sediment content, and three hydraulic loads. At each pollutant load, different hydraulic loads were implemented by adjusting the inlet and outlet water flow rates. High-throughput sequencing was used to investigate the relationship between microbial community and function of the system, as well as the mechanisms underlying the biological removal of nitrogen and phosphorus under different conditions. 【Result】 ① The purification was the best when the filter system was 80 cm high, and the least when the filter height was 40 cm, with the height of 60 cm in between. For each filler combination, the system worked the best when the volumetric ratio of coarse sand, activated carbon and clay ceramsite was 3∶2∶2 and the filler height was 80 cm. Under these conditions, the removal rates of total nitrogen (TN), total phosphorus (TP), ammonia nitrogen (AN) and sediment were 53.26%, 82.51%, 68.18% and 78.43%, respectively. ② The purification of TN was the best when the pollutan load was 2 mg/L (W1), followed by pollutant load of 4 mg/L (W2), with their removal rates being 56.70% and 42.78%, respectively. The purification of TP, AN and sediment were the best when AN concentration was 4 mg/L and sediment content was 0.2 g/L, with their removal rates being 48.46% and 81.61%, respectively. Pollutant load did not have a significant impact on TP purification. ③With the increase in hydraulic load, the removal efficiency of TN, TP, AN and sediment decreased. The hydraulic load of 28 L/(m2·min) (T1) worked the best for purifying TN, TP, AN and sediment, with their removal rates being 48.80%, 78.51%, 54.88% and 79.77%, respectively. ④ The number of bacterial species was higher in the lower part of the filtration columns, while the bacterial community was more diverse in the upper part of the columns. The microbial community was similar in columns in which the filler combinations were similar. It was found that Proteobacteria was most abundant, followed by Actinobacteria and Bacillota, all being efficient in immobilizing nitrogen. 【Conclusion】 Packing the media in strata to the height of 80 cm with the volumetric ratio of coarse sand, activated carbon, and clay ceramsite being 3∶2∶2 was most effective for purifying the farmland drainage water. When the pollutant load of TN, AN and sediment was 2 mg/L, 4 mg/L, and 0.1 g/L to 0.3 g/L, respectively, and the hydraulic load was 28 L/(m2·min), the system was most efficient for removing the pollutants.

Keywords

• farmland drainage
• artificial rapid percolation system
• packing combination
• operation management
• purification mechanism