Study On Removal Of Nitrogen And Phosphorus From Sewage By Non-metallic Minerals-struvite Composite Precipitation

As most precious studies,the supernatant mixture of sludge thickening tank still contain most nitrogen?N?and phosphorous?P?which need to be further removed.So the supernatant mixture of sludge thickening tank from the municipal sewage treatment plant is often returned to the front of the biochemical treatment unit.And the content of nitrogen and phosphorus in the supernatant mixture of the sludge thickening tank have effect on the nitrogen and phosphorus load of effluent in the subsequent biochemical treatment system.Here,taking the simulated wastewater and the supernatant mixture of the sludge thickening tank as research objects,and using non-metallic minerals-struvite composite precipitation method,the suitable removal conditions and removal efficiency of nitrogen and phosphorus were discussed in the simulated wastewater and the supernatant mixture of the sludge thickening tank.The main results of this thesis were as follows:The suitable reaction conditions for removing nitrogen and phosphorus from simulated wastewater by struvite precipitation approach were pH of the wastewater with 9.5,the reaction time with 60 min,and the temperature with indoor temperature?because the temperature was not main driving factor effected on nitrogen and phosphorus removal efficiency in the whole treatment process?.The suitable reaction conditions for removing nitrogen and phosphorus from the supernatant mixture of sludge thickening tank by struvite precipitation method were pH of the wastewater with 9,the reaction time with 60 min,and the temperature with indoor temperature.Under suitable reaction conditions,the removal rate of NH₄⁺-N and PO₄^3--P in the supernatant mixture of sludge thickening tank were14.33%and 22.71%,respectively.Keeping the initial concentration of NH₄⁺-N and Mg²⁺of the supernatant mixture of sludge thickening tank as fixed values,and taking into account the influence of residual concentration of PO₄^3--P in wastewater,it was not appropriate to increase the initial concentration of PO₄^3--P to promote the precipitation reaction.This conclusion was consistent with the result of simulated wastewater.When the initial concentration of NH₄⁺-N and PO₄^3--P in the simulated wastewater was kept close to that of the supernatant of the sludge thickening tank,the removal effects of NH₄⁺-N and PO₄^3--P were 38.04%and 50.48%through increasing the molar ratio of Mg²⁺to PO₄^3-up to 3.75:1.However,Keeping the initial concentration of NH₄⁺-N and PO₄^3--P of the supernatant mixture of sludge thickening tank as fixed values,the removal rates of NH₄⁺-N and PO₄^3--P were 22.75%and 35.94%through increasing the molar ratio of Mg²⁺to PO₄^3-up to 2.5:1.Non-metallic minerals-struvite composite precipitation was used to dispose simulated wastewater.Under the condition of adding magnesium source,the three natural non-metallic minerals including zeolite,diatomite and vermiculite were added into simulated wastewater,the natural zeolite was more suitable for the treatment of nitrogen and phosphorus in wastewater.When the natural zeolite dosage was 10g/L,the removal effect of NH₄⁺-N and PO₄^3--P was better,and the removal rates of NH₄⁺-N and PO₄^3--P were 33.58%and 34.33%,respectively.Under the condition of adding magnesium source,the three modified non-metallic minerals including zeolite,diatomite and vermiculite were added into simulated wastewater,the modified diatomite was more suitable for the treatment of nitrogen and phosphorus in wastewater.When the modified diatomite dosage was 10g/L,the removal effect of NH₄⁺-N and PO₄^3--P was better,and the removal rates of NH₄⁺-N and PO₄^3--P were34.46%and 48.4%,respectively.The removal efficiency of NH₄⁺-N and PO₄^3--P in simulated wastewater by the addition of modified non-metallic minerals system was slightly better than that of the non-metallic minerals system.Modified zeolite,diatomite and vermiculite were used to dispose the supernatant mixture of sludge thickening tank.The pH value of the wastewater system gradually increased with the increase of the non-metallic mineral dosage amount.From the aspects of removal efficiency of NH₄⁺-N and PO₄^3--P and the effect on the pH value change of wastewater,modified diatomite was more suitable for the treatment of nitrogen and phosphorus in the supernatant of sludge thickening tank based on above results.When the modified diatomite dosage was 10g/L,the optimal removal rates of NH₄⁺-N and PO₄^3--P were 34.93%and 66.67%,respectively.The treatment of the supernatant mixture of sludge thickening tank by non-metallic minerals-struvite composite precipitation method can reduce the nitrogen and phosphorus in the return supernatant mixture of sludge thickening tank.It could be used for the recovery of nitrogen and phosphorus in future.The nitrogen and phosphorus load of the subsequent treatment process will be reduced at the same time.And the modified diatomite precipitated sludge containing nitrogen and phosphorus produced by the purification system can be utilized as a resource for nitrogen and phosphorus fertilizer.