Study On Filtration Performance And Backwashing Conditions Of Two Types Of Modified Sand Materials

Using two new types of coated iron oxide sand (Nano-Iron Oxide Coated Sand, denoted as "Nano-OCS"; iron oxide modified sand, denoted as "IOCS"), Raw Quartz Sand (denoted as "RQS") and activated carbon to do static adsorption experiment and filter tests and backwash regeneration test. Were investigated Nano-OCS adsorption of ammonia; two new types of coated iron oxide sand and RQS removal of humic acid (denoted as "HA") under different experimental conditions, and activated carbon adsorption rates were compared; Study of RQS、IOCS and Nano-OCS adsorption efficiency to HA and turbidity in raw water and its backwash regeneration conditions.. The results showed that:(1) Under conditions of raw water PH<7, its volume of150mL, vibration time was1.5h, the initial ammonia concentration is1.53mg/L, Nano-OCS to20g and vibration strength is70r/min, Nano-OCS’adsorption rate of ammonia nitrogen is up to26.6%. Each test conditions affect the effect of the test results as follows:the raw water ammonia concentration> vibration time> weight modified sand> raw water PH and vibration strength. Nano-OCS direct filter ammonia is better than RQS.(2) Nano-OCS, IOCS and RQS achieve optimum effect of absorption conditions are: vibration time3h, the initial concentration of HA1.5mg/L, Water-sand ratio1.5and vibration strength180r/min. Under optimal conditions, all the material removal rate of HA were60%,77.1%and43.8%. In which, Nano-OCS adsorption of HA descending vibration factor:the initial HA concentration> water-sand ratio> concussion time> vibration strength; IOCS adsorption of HA vibration factor descending as:the initial HA concentration> water-sand ratio> vibration strength> vibrationk time; vibration factor descending RQS of HA adsorption is:vibration strength> initial HA concentration> vibration time> Water-sand ratio.(3) Under the above optimum conditions (except vibration time), the study of Nano-OCS, IOCS, RQS and activated carbon continuously adsorption of HA were done. The rule of each filter adsorption of HA on the overall strength capacity is:Activated Carbon> Nano-OCS> IOCS> RQS, where the highest removal rates were as follows: 88.1%,63.5%,54.2%and30.8%.(4) For Nano-OCS and IOCS, their filtration efficiencies to HA and turbidity and optimum backwashing conditions were studied. Their filtration and backwashing properties were compared with those of RQS. The results are:①When thickness of filter media layer is45cm, the optimal filtration velocity is6m·h-1;②Three kinds of media efficiency to HA and turbidity is in the following order:Nano-OCS> IOCS> RQS. The highest removal efficiency of Nano-OCS and IOCS to HA is71.70%and61.61%respectively.③The best backwash conditions of Nano-OCS and IOCS is:First, sands are kept soaking in NaOH solution with concentration0.5mol·L-1and backwashing intensity with air is13L·(s·m)-1which lasts6mins; Second, backwashing with NaOH solution whose concentration is0.075mol·L-1and air at the same time. Their backwashing intensity is8L·(s·m2)-1and13L·(s·m2)-1separately. Backwashing time is3mins; Third, backwashing with air and0.015mol·L-1concentration of FeCl3solution together; Their backwashing intensity is8L·(s·m)-1and13L·(s·m)-1respectively. Backwashing time is2mins; Finally, backwashing with clean water is4mins, whose intensity is8L·(s·m2)-1.(5) When the thickness of the filter media layer increases from45cm to60cm, the average direct filtration efficiency of Nano-OCS and IOCS to HA by56.1%and45.8%increase to57.5%and47.9%; When the filter layer thickness increased to80cm, the average removal rate of63.8%and52.6%.Increase the filter layer can significantly enhance the effect of the removal of HA. Filter layer thickness changes, the best conditions are changed backwashing. For Nano-OCS and IOCS, their surface morphological structures are more complex and rough, the porosity on the surface increases after backwashing compared with those on the surface of RQS.Removal efficiency to HA is enhanced.