Study On Strengthening Coagulation With Adsorbent To Remove Secondary Effluent Pollutants From Wastewater Treatment Plant

The secondary effluent of urban sewage treatment plant has become a major way of efficient utilization of water resources through advanced treatment.Landscape environment recycling is the main part of renewable water utilization.The utilization of low energy consumption physicochemical metho d for advanced treatment of secondary effluent is a necessary step to achieve pollutant reduction and low concentration discharge of nutrient elements.In this study,eight kinds of green,cheap and easy to get powders,such as PAC,biochar,mullite,walnu t shell,FeOOH,PAC loaded FeOOH,zeolite loaded FeOOH,Natural oblique zeolite were compared,to explore the effect of adsorbent on the removal of pollutants from the secondary effluent,the effect of adsorbent as coagulant aid to strengthen the coagulation of PACl to reduce pollutants from the secondary effluent,and to evaluate the efficient operation of coagulant and powder adsorbent in the same reaction unit.In the simple adsorption experiment of adsorbent,the raw water is the effluent from the secondary sedimentation tank of the AAO small-scale test device operated in the laboratory.Eight kinds of adsorbents are adsorbed for 2 hours in the speed of 200 rpm at room temperature,and the decontamination performance of different doses of adsorbents is investigated.It is found that different powder adsorbents have different decontamination advantages.The first batch of powdery adsorbents?PAC,biochar,Molai powder,walnut shell powder?are commercially available materials,with adsorption doses of 50mg/L,75 mg/L,100 mg/L,125 mg/L and 150 mg/L;the second batch of powdery adsorbents are self-made hydroxy iron oxide series adsorbents?FeOOH,PAC loaded FeOOH,zeolite loaded FeOOH,compared with PAC and zeolite adsorption?,with dosage of 25 mg/L,50 mg/L and 75 mg/L?100 mg/L?150 mg/L?200 mg/L?Biochar and PAC can reduce UV₂₅₄ and DOC.PAC of 150mg/L can remove 69% and 24.8% of UV₂₅₄ and DOC respectively.DOC concentration is reduced from 5.89mg/L to 4.43mg/L and biochar is weaker than PAC.Walnut shell powder and mullite powder of 150mg/L can remove 15.2% and 10.3% of TP respectively,which is weaker.FeOOH of 200mg/L can reduce TP concentration from 0.95mg/L to 0.29mg/L,and the removal rate is 69.2%.PAC loaded FeOOH of 200mg/L can reduce TP concentration from 0.95mg/L to 0.40mg/L,and the removal rate is 58.2%.The removal rates of UV₂₅₄ and DOC by PAC loaded FeOOH were 65% and 35%,respectively.The adsorption behavior of FeOOH and PAC loaded FeOOH tends to be chemical adsorption.The FTIR spectrum and SEM observation before and after the adsorption of the series of iron hydroxide adsorbents show that the characteristic adsorption of FeOOH on phosphate and PAC loaded FeOOH on organics and phosphates takes place.In the experiment of adsorbent enhanced coagulation,the aforementioned powdery adsorbent is used as coagulant aid of PACl in the flocculation stage,and the dosage of PACl is 50mg/L.PAC of 125mg/L can improve the removal rate of 45% DOC by coagulation alone to 95%.50 mg/L PAC can reduce the remaining fluorescent substances after PACl coagulation to the detection limit.PAC loaded FeOOH of 150 mg/L can increase the removal rate of UV₂₅₄ and DOC by 46% and 38% on the basis of coagulation.FeOOH and PAC loaded FeOOH of 150 mg/L can improve the removal rate by 70% and 60% on the basis of coagulation,and achieve the TP concentration of effluent less than 0.2mg/L.To sum up,coagulant is put into the mixing stage of the coagulation reaction tank,and adsorbent is put into the flocculation stage to assist the coag ulation,so that the coagulation and adsorption can be carried out s ynchronously in the same place.PAC loaded FeOOH powder adsorbent and PACl can remove organic pollutants,TP and fluorescent pollutants in the secondary effluent,which can meet the standa rds of landscape water reuse and discharge phosphorus with ultra-low concentration?less than 0.2mg/L?.