Study On Constructed Rapid Infiltartion System For Wastewater Treatment

Though wastewater Rapid Infiltration (RI) land treatment system has the advantages of requiring simple equipment, easy to operate, low-cost constructing and operating, low energy consuming and having a good effluent quality, it also has the disadvantages of low Hydraulic Loading and demanding large land area coverage. So its application is restricted. Constructed Rapid Infiltration (CRI) system is a brand wastewater treatment system that has been developed from the traditional RI system. The study of CRI is just in the initial stage in China, and many of its aspects need to be further studied. Based on this consideration and combined the current situation in domestic and abroad, a detailed research on CRI has been conducted from lab-scale experiment to on-site experiment and finally to practical engineering.The lab-scale CRI systems have been designed to treat bath wastewater and domestic wastewater by adopting artificial quartz and alluvial sands. The effects of operation pattern and workmanship upon the pollutant removal effect of CRI have been studied at a higher Hydraulic Loading (HL) condition. The results show that CRI has quite different removal effect by using two different Hydraulic Loading Cycles (HLC) at the same HL (1.49-2.12 m/d) condition: the average removal rates for CODCr, BOD5 and LAS are 80.33% and70.18%, 82.44% and 55.75%, 90.86% and 85.28% respectively; the average concentrations of CODcr, BOD5 and LAS in the treated effluent are 16.09 and 24.40 mg/L, 6.08 and 15.33 mg/L, 0.18 and 0.29 mg/L respectively. The study on domestic wastewater also conducts the same results, that is, by shortening HLC of CRI system, the oxygen recovery rate is increased, the Hydraulic Residence Time (HRT) is lengthened and the removal effect of the system is significantly improved. In the light of the low Hydraulic Loading of traditional wastewater rapid infiltration system, an experiment project of constructing composite system by adopting artificial quartz and alluvial sands is put forward. A lab-scale experiment has been conducted with bath wastewater. The results show that the composite system has a better removal effect for bath wastewater at the HL condition of 2.31 m/d. The average removal rates for CODcr, BOD5 and SS are 86.25%, 86.75% and 98.95% respectively; the average concentrations of CODcr, BOD5 and SS in the treated effluent are 17.80, 5.84 and 0.3 mg/L respectively.The on-site experiment has been designed to treat polluted river water by adopting alluvial sands. The removal effects of CRI system on CODcr, BOD5, SS, NH3-N, LAS, T-N and T-P and the clogging situation of the system are mainly discussed. The results show that the average removal rates for CODcr and BOD5 are 80% and 85%; for SS, NH3-N and LAS are all more than 95%; and for T-N and T-P are quite low. Study on the clogging problem of CRI system show that the accumulating of organic suspended material in top medium of the rapid infiltration tank is the main reason for clogging.The engineering results show that CRI system has a better pollutant removal effect for domestic wastewater. The average removal rates for SS, CODcr and BOD5 are 94.58%, 90.17% and 94.44% respectively; the average concentrations of SS, CODcr, BOD5, NH3-N and LAS in the treated effluent are 4.07, 23.20, 9.0, 5.16 and 0.29 mg/L respectively. Adopting the operation pattern of intermittent flooding-drying avoids the pollutant breakthrough because of high HL and pollutant loading, solves the clogging problem, and guarantees the steady running of CRI system at a higher HL (1 m/d) condition.Results from lab-scale experiment, on-site experiment and engineering practice show that the CRI system not only surmounts the shortcoming of having a low HL of the traditional RI system, but also reserves the advantages of simple, low-cost constructing, low energy consuming and having a good effluent quality. And it has a wide developing prospect.