Water Quality Analysis And Treatment Technology Study Of Wastewater From Algae Waste Dewatering Process

Eutrophication of water can lead to cyanobacteria eruption,causing serious ecological and health hazards.At present,large-scale management of blue algae is still“salvage,dehydration,burning”.The dehydration of cyanobacteria is a complex system engineering,which can produce wastewater with great difference of water quality and quantity at many nodes,such as the drainage of cyanobacteria water separation station and cyanobacteria mud pressure filtrate.Among them,the concentration of water quality indexes of algae water separation station is low,but the amount of water is large.The wastewater produced by the subsequent pressure filtration of cyanobacteria mud has high salt concentration,complex species and biological inhibitive substances.The purpose of this study is to explore the water quality characteristics of various kinds of wastewater,to develop the combined process suitable for the treatment of various cyanobacteria wastewater,and to evaluate the actual wastewater treatment effect.（1）The water quality characteristics of the drainage of cyanobacteria water separation station,the pressure filtrate of cyanobacteria mud at normal temperature and the hot pressure filtrate of cyanobacteria mud at high temperature were analyzed,including conventional water quality monitoring indicators such as COD,TN,NH₄⁺-N and TP,metal ions(Ca²⁺,Fe³⁺,etc.)and organic component analysis based on LC-MS/MS.The COD,TN,NH₄⁺-N and TP are6-159 mg/L,0.67-16.73 mg/L,0.16-8.85 mg/L and 0.01 mg/L,respectively.The COD,TN,NH₄⁺-N and Ca²⁺of the pressure filtrate at room temperature are 2000-8000 mg/L,300-750mg/L,250-700 mg/L and 1000-4000 mg/L,respectively.The contents of TN,NH₄⁺-N,COD,TP,total sugar,protein and Fe³⁺in the high-temperature pressure filtrate of cyanophylla mud are 1842.33±154.62 mg/L,1742.56±124.65 mg/L,15678.33±784.26 mg/L and 29.85±1.25mg/L,845.00±2.50 mg/L,11.10±0.05 g/L,4761±5 mg/L,respectively.Through the LC-MS/MS analysis of the pressure filtrate of cyanobacteria mud at room temperature and high temperature,it can be found that there are macromolecules which are difficult to degrade in the pressure filtrate of cyanobacteria mud,such as arylalkyl ketones,carboxylic acids and phenols.In general,there are great differences in the water quality of the three types of cyanobacteria wastewater,among which the pollution degree of the drainage of the cyanobacteria water separation station is low,which requires ultra-low discharge.The normal temperature pressure filtrate of cyanobacteria mud has high concentration of organic matter,rich in metal ions(Ca²⁺,Fe³+,etc.),biological inhibition and extremely alkaline.Compared with the normal pressure filtrate,the high temperature hot pressure filtrate of cyanobacteria mud has higher organic matter concentration（about 2-3 times）,high metal ion(Fe³⁺)content,and extremely acidic.The biodegradability of the two kinds of cyanobacteria mud filtrate was low.（2）The combined process of“powdered activated carbon-membrane bioreactor-sulfur autotrophic denitrification filter”（PAC-MBR+SAD）was constructed to treat the drainage of algae water separation station.Through parameter optimization of PAC-MBR,the optimal parameters for the drainage of cyanobacteria water separation station were determined as follows:DO was 3.5-4.5 mg/L,HRT was 4 h,and PAC dosage was 2 g/L.Under these conditions,the removal rates of COD,TN and NH₄⁺-N are 66.00%,93.75%and 95.71%,respectively.Two different sulfur autotrophic denitrification filters（SAD）were compared,namely,the sulfur and calcium mixed sulfur autotrophic denitrification filter（SL-SAD,sulfur:limestone=3:1）and pure sulfur autotrophic denitrification filter（S-SAD,filled only with sulfur particles）.The results showed that both SL-SAD and S-SAD could remove more than98%nitrate at 3 h HRT,showing a good autotrophic denitrification and nitrate removal performance.Compared with traditional SL-SAD,S-SAD showed a better denitrification performance（more than 98%）,confirming that controlling the dosage of basicity adjustment is a feasible method to regulate the degree of s-SAD denitrification.The TDS and sulfate in the effluent of S-SAD were significantly lower than those of SL-SAD.Prediction analysis of microbial community structure and function showed that the relative abundance of denitrifying microorganisms such as thiobacillus sp.S-SAD was high.Thiobacilhus and Thermomonas are the main microorganisms in SL-SAD and S-SAD.The relative abundance of Thiobacillus and Thermomonas is higher in S-SAD compared to SL-SAD,indicating that S-SAD has better denitrification performance.（3）Based on the characteristics of high concentration of NH₄⁺-N in the pressure filtrate at room temperature,extremely alkaline wastewater（p H>11）and poor biodegradability,the pretreatment processes of stripping and Fenton oxidation were proposed.In the continuous flow stripping experiment with a stripping rate of 60 L/min and a stripping time of 0.5 h,the NH₄⁺-N removal rate of 26.67%can be achieved,reducing the pressure of subsequent biological nitrogen removal.In addition,the subsequent treatment of the exhaust gas was successfully solved by sulfuric acid solution.The Fenton oxidation process was optimized to treat the pressure filtrate of cyanobacteria mud at room temperature.The optimized process parameters are as follows:Fe SO₄·7H₂O/COD is 1.0,optimal H₂O₂/COD is 1.5,optimal reaction time is 90 min and p H is 2.Under these conditions,the B/C of the cyanobacteria filtrate could be increased from 0.21 to 0.78.The Fenton oxidation process was used to treat cyanobacteria mud with high temperature pressure filtrate（p H<3）and low biodegradability.Optimized parameters:Fe SO₄·7H₂O/COD is 1.5,the optimal H₂O₂/COD is 1.5,and the optimal reaction time is 120 min.The biodegradability of the two cyanobacteria mud-pressurized filtrates was improved by pretreatment,and the B/C was increased from 0.21to 0.78.（4）The cyanobacteria mud pressure filtrate after physical and chemical treatment is used as the influent of biochemical treatment unit to construct“UASB+two-stage A/O”for the detoxification,decarburization,nitrogen removal and phosphorus removal of the cyanobacteria wastewater.After optimization of key parameters such as load lifting,DO and glucose addition,the UASB-two-stage A/O combined process can handle the cyanobacteria mud pressure filtrate well,and the effluent water quality can meet the standards for discharging into the municipal pipe network.The optimized physical and chemical processing parameters were obtained according to the above mentioned,and the continuous operation of the combined process was realized,which was used to treat the actual cyanobacteria pressure filtrate.In the continuous operation process,the HRT and the carbon source input of the two-stage A/O unit are further optimized for UASB.The effluent water quality of COD,TN,NH₄⁺-N and TP are 375.67±23.12 mg/L,51.23±2.52 mg/L,35.44±1.14 mg/L and 3.52±0.22mg/L,respectively.The effluent from the combined process meets the water quality Standard for Sewage discharged into urban sewer（GB/T31962-2015）.（5）Material balance and economic feasibility analysis were conducted on the process of“powder activated carbon-membrane bioreactor+sulfur autotrophic denitrification filter”（low concentration cyanobacteria wastewater treatment process）and“physicochemical+UASB+two-stage A/O”（high concentration cyanobacteria pressurized filtrate treatment process）.The direct treatment cost of the“PAC-MBR+S-SAD”process proposed in this study is about 39.62 yuan/ton.If it is applied to the treatment of all the salvage blue algae in this city,it can reduce the discharge of 66.0%COD,93.7%TN,95.7%NH₄⁺-N and 80.0%TP,It is equivalent to the reduction of COD,TN,NH₄⁺-N,TP emissions by 4000-7000 kg,900-1600kg,800-1450 kg,100-170 kg,respectively.The direct cost of water treatment in the process of“physicochemical+UASB+two-stage A/O”is 86.345 yuan/ton.If the combined process is adopted,the discharge of 98.0%COD,97.4%TN,98.1%NH₄⁺-N and 89.3%TP can be reduced.It is equivalent to reducing the emissions of COD,TN,NH₄⁺-N and TP by7500-13500 tons,900-1600 tons,850-1550 tons and 12-22 tons,respectively.