Study On Filtration Performance Of Two New Types Of Modified Filter Materials To HA And Backwashing Conditions Optimization

In this paper, the filtration and backwash process conditions of two new types of modified filter materials - Iron Oxide Coated Sand (IOCS for short) and Nano-iron Oxide Coated Sand (Nano-OCS for short) to remove HA were optimized.First of all, without a filter aid, when the turbidity of water before filter is changed, filter and backwash experiments of two new types of modified filter materials whose filter layer thickness is 80 cm showed that:(1) the condition of the turbidity of water before filter and backwash parameters optimal combination is:In the stage of soaking with air backwashing, modified filter materials are kept soaking in NaOH solution with concentration 0.3 mol/L and backwashing intensity of air is 12 L/(s-m2) which lasts 3 mins. In the stage of air-liquid backwashing, backwashing intensity of air and liquid is 13 L/(s·m2) and 8 L/ (s·m2) respectively, backwashing with NaOH solution whose concentration is 0.025 mol/L and air at the same time which lasts 3 mins, then backwashing with FeCl3 solution whose concentration is 0,015 mol/L and air at the same time which lasts 2 mins. In the stage of clean water backwashing, backwashing with clean water whose intensity is 8 L/(s·m2) for 5 mins. At the beginning of the filter, the turbidity of water before filter is controlled in the range of 1±0.25 NTU. (2)Under the condition of the optimal combination, average removal rate of IOCS and Nano-OCS to HA is 48.76% and 59.68% respectively, and the highest removal rate reaches 80.58% and 84.64% separately. (3) Under the condition of the optimal combination when the filtration velocity is changed, and the best filtering velocity is 6 m/h.Secondly, when the filtration velocity is 8 m/h, by adding different doses of filter aid PAC, under the condition of the optimal combination, filter and backwash experiments of two new types of modified filter materials whose filter layer thickness is 80cm showed that: (1) the PAC optimal dosage is 0.80 mg/L. (2)Under the condition of PAC optimal dosage, the average removal rate of IOCS and Nano-OCS to HA are 72.29% and 73.69% respectively, and the highest removal rate reach 79.09% and 82.17% separately, and the average removal rate of IOCS and Nano-OCS to turbidity are 68.03% and 69.65% respectively, and the highest removal rate reach 73.21% and 73.64% separately.Finally, when the filter layer thickness was increased to 100 cm, the result of filter and backwash experiments of two new types of modified filter materials whose filter layer thickness is 100 cm with a filter aid PAC showed that:(1) The condition of the PAC dosage and backwash parameters optimal combination is:In the stage of soaking with air backwashing, modified filter materials are kept soaking in NaOH solution with concentration 0.1 mol/L and backwashing intensity of air is 12 L/(s·m2) which lasts 3 mins. In the stage of air-liquid backwashing, backwashing intensity of air and liquid is 13 L/(s·m2) and 8 L/ (s·m2) respectively, backwashing with NaOH solution whose concentration is 0.050 mol/L and air at the same time which lasts 3 mins, then backwashing with FeCl3 solution whose concentration is 0.015 mol/L and air at the same time which lasts 2 mins. In the stage of clean water backwashing, backwashing with clean water whose intensity is 8 L/(s·m2) for 5 mins. At the beginning of the filter, the PAC dosage is set to 1.1 mg/L. (2) Under the condition of the optimal combination, the average removal rate of IOCS and Nano-OCS to HA are 65.32% and 68.60% respectively, and the highest removal rate reach 75.57% and 78.94% separately, and the average removal rate of IOCS and Nano-OCS to turbidity were 70.90% and 73.31% respectively, and the highest removal rate reach 85.71% and 87.39% separately. (4) When the thickness of the filter media layer increases from 80 cm to 100 cm, the filtration cycle of IOCS and Nano-OCS can be doubled and extended to more than 40 h, the difference of their optimal backwash parameters is the concentration of NaOH solution in the stage of soaking with air backwashing and the stage of air-liquid backwashing. The removal effect of Nano-OCS to HA and turbidity is better than that of IOCS under different conditions.