Research On Modified Attapulgite Treating Source Water With High Colour And High Ammonia Nitrogen At Low Temperature

In the situation of executing the new Hygienic Standard for Drinking Water （GB5749-2006）, according to the poor treatment effects for conventional technologies inwater plants, attapulgite from Xu Yi in Jiang Su was modified in this subject to developnew ballasted flocculant-adsorbent and molecular sieve. The reaction mechanisms wereexplored from kinetics and substance transformations through characterizations oftesting instruments, the surface complexation-adsorption-flocculation theory andorthogonal-response surface methodology were applied, the integration technology of“ballasted flocculation-high efficient sedimentation-precoating membrane filter” basedon modified attapulgite was studied for colour and NH₄⁺-N removal. The subjectprovided feasible plans and technical support about drinking water safety.Analyzed the microstructure, characteristics and formation mechanisms ofmodified attapulgite by X-Ray Spectra （XRF）, X-Ray Diffraction （XRD）, FourierTransform Infrared Spectroscopic （FT-IR）, Scanning Electron Microscope（SEM）, BETSurface Area and Pore Size Distribution. Studied on attapulgite modification methodsfor colour and NH₄⁺-N removal in source water at low temperature.The results showthat decoloration efficiency of Chitosan/Purified Attapulgite（CPA） is the mostsignificant, the mechanism is mainly electrostatic adsorption and chemical reaction. Thedecoloration efficiency of purified attapulgite takes second place, instead, thermal andacidified attapulgite cause colour increase; NH₄⁺-N removal effect of alkalifiedattapulgite （4A molecular sieve） is the most significant，the mechanism is mainly ionexchange. NH₄⁺-N removal rate is low for thermal and acidified attapulgite, CPA can’tremove NH₄⁺-N. Above results have great scientific significance for correctlyunderstanding nanometer effects of attapulgite.Based on the related parameters of adsorption isotherms, adsorption kinetics andthermodynamics, the adsorption properties at low temperature were studied, includingHA adsorption on CPA, NH₄⁺-N and HA adsorption on4A molecular sieve forNH₄⁺Cl-HA coexisting solutes. The results indicate that HA adsorption process on CPAis controlled by film and pore diffusion. The adsorption equilibrium is well described byLangmuir-Freundlich equation, the maximum adsorption capacities （qe,max） is120.7731mg/g. NH₄⁺-N and HA adsorption on4A molecular sieve are in accord with Freundlichequation, is mainly concerned with intra-particle diffusion. qe,maxwas61mg/g and21mg/g, respectively. NH₄⁺-N adsorption on4A molecular sieve depends on ionexchange, molecular dispersion force, induction force and electrostatic adsorption. HA in solution could inhibit NH₄⁺-N adsorption on4A molecular sieve. HA adsorption on4A molecular sieve depends on electrostatic adsorption, cationic bridge, complexationbetween HA and hydroxyl compounds produced from aluminum salts on the surface of4A molecular sieve. NH₄⁺-N in solution could promote HA adsorption on4A molecularsieve. CPA and4A molecular sieve are more appropriate for treating source water at lowtemperature in North. In addition, CPA and4A molecular sieve own strong regenerationcapacity and can be recycled. Above results provide theoretical basis for developmentand application of the adsorbents, and have great economic significance.Studied treatment efficiency and coagulation mechanisms of high-colour source water at low temperature, used central composite design of responsesurface methodology to determine the optimal combination of enhanced coagulationwith “returning sludge-PFA-CPA”. The results show that, the significant factorsaffecting colour removal are pH and returning sludge yield. HA-particles mainly makecomplexing reactions with hydrolysates of PFA. CPA can effectively remove dissolvedorganic matter. CPA as condensation nuclei increase flocs’ strength and particle size,and improve the recovery ability of broken flocs. Returning sludge can improveobviously low-turbidity state and bring HA adsorption on CPA into play. After enhancedcoagulation, the effects of water colour and temperature on each index removal are notobvious. Above results provide technical supports for optimal operation and debugging.Explored the optimal operation method on “new Densadeg-precoating membranefilter of4A molecular sieve” technology, investigated the effluent quality from each cell.The results show that, control sludge return ratio to ensure the suspended solid （SS）values in mixing tank are in the range of498⁹00mg/L, high-concentration SS values inmixing tank may greatly reduce coagulant dosages. Controlled accurately emissionamount of sludge and sludge-water interface under inclined plate in Densadeg, so as toensure sludge-water interface low and bottom sludge concentration high. The newDensadeg efflument has no obvious change for hydraulic loads lower than50L/h andorganic matters lower than8mg/L in source water. The precoating membrane filter of4A molecular sieve formed in the optimum conditons was used to filtrate the effluentfrom Densadeg, NH₄⁺-N removel rate reaches the highest to95%. Basement membraneadopts physical cleaning and is changed every34days. The “new Densadeg-precoatingmembrane filter of4A molecular sieve” technology have significantly effects ontreating source water from Qing Ding reservoir at low temperature. Above resultsprovide feasible theories and technical supports for industrialization promotion.