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Increased pollution caused by socio-economic development has led to compound-contaminated high-hardness water pollution. In this study, laboratory-scale nanofiltration (NF) treatment of such water was investigated. Response-surface methodology was used to optimize the NF operating parameters, and a regression model with desalination rate and transmembrane pressure changes as response values was established. The NF membrane efficiencies in contaminant removal from groundwater and surface water with compound-contaminated high hardness and the membrane-fouling characteristics during long-term operation were investigated. The results show that the optimal operating parameters for the NF membrane in the removal of inorganic salts from groundwater are as follows: influent pH 8, influent pressure 1 MPa, and water yield 27.976%. The removal rates for groundwater total hardness, total alkalinity, total soluble solids, K+, Na+, Ca2+, Mg2+, , Cl−, , and were 99.4, 90.3, 84.7, 63.2, 56.8, 99.6, 95.2, 99.6, 68.3, 86.1, and 65.9%, respectively. Surface water contains more complex components; therefore, membrane fouling during surface water is more serious. The NF membrane was operated continuously for more than 35 days under the optimal operating conditions with no serious membrane fouling. HIGHLIGHTS Response-surface methodology was used to optimize the NF operating parameters.; NF membrane was operated continuously for more than 35 days under the optimal operating conditions with no serious membrane fouling.; The membrane fouling by hardness ion was analyzed by SEM-EDS.

The countercurrent–cocurrent dissolved air flotation (CCDAF) process is a new type of air flotation process integrating countercurrent collision and cocurrent flow adhesion processes. The structural form of the CCDAF tank and its process parameters are the required conditions to achieve countercurrent collision and cocurrent adhesion. In this study, eight CCDAF tank process models were established with a flow rate of 0.5 m3/h. Flow field numerical simulation and process optimization of a CCDAF tank was conducted using Fluent software. The simulation results show that the optimal conditions for the CCDAF process are as follows: contact zone ascending velocity 10 mm/s, separation zone separation velocity 1.5 mm/s, dissolved gas pressure 0.45 MPa, and recirculating dissolved-gas distribution ratio R1/R2 1:1. Under these operating conditions, the flow state in the flotation tank is the most stable and the gas in the contact zone is evenly distributed. According to the simulation results, a 5 m3/h pilot plant was built. The structural dimensions were: B × L × H = 1,020 mm × 1,300 mm × 1,350 mm. The test results show that the CCDAF has a significant decontamination effect and is clearly superior to the cocurrent flow DAF process and countercurrent flow DAF process.

As the water diversion reservoir showed high organic matter and high algae in summer, the potassium permanganate pre-oxidation/dissolved air flotation/carbon sand double filter process was developed. The test results show that the optimum operation conditions of the combined process were as follows: the dosage of KMnO4 was 0.3 mg/L, the dosage of polymeric aluminum ferric chloride (PAFC) was 3.0 mg/L (Al3+), the reflux ratio was 10%, and the dissolved gas pressure was 0.3 Mpa. Taking Ji'nan Queshan reservoir water algae pollution as the research object, the average removal rate of chlorophyll a, blue-green algae, turbidity, particle number and total organic carbon (TOC) reached 66.64%, 95.44%, 94.45%, 99.34% and 46.68%, respectively; the methylisoborneol (MIB) removal rate was 92.47%, the odor level decreased with process flow from raw water level 4 to effluent level 1.5, geosmin (GSM) dropped below the detection limit, and the total removal rate of trihalomethane formation potential (THMFP) was 33.56%. The effluent of the combined process meets the requirements of the Hygienic Standard for Drinking Water (GB5749-2006) after it is disinfected.