Research On The Microfiltration For Retention Of Algae In Algal-bacterial Symbiotic Wastewater System

Water pollution and energy crisis has threatened to the sustainable development ofhuman society. For biodiesel as a green generation of energy is widely concerned, inthe meantime algae with high oil yield is considered to be the preferred source of rawmaterials for biodiesel production. Therefore, the use of urban sewage cultivating high-fat microalgae to achieve wastewater treatment and resources recycling is the best way.Based on this situation, the research group developed the new algal-bacteria symbioticreactor. But an effective and low-cost algae retention process has not been found. In theoriginal algal-bacteria symbiotic reactor, since algae residence time is too short can leadto rapid algae growth. In solve to solve this problem, this study proposed solution usingmembrane retention of algae in the algal-bacteria symbiotic reactor.After theoretical analysis, literature consult and market research, four kinds of cross-flow type membrane modules and 4 dead-end type membrane modules were selected forthe study. By comparing algae retention performance of the membranes, the optimizedmembrane and operating conditions were found. In the lab scale experiment, each mem-brane algae retention performance was investigated, and we got the following results:(1) The algae retention rate of 8 membranes with the nominal pore size below 1.2μmcould reach to 100%.In the 4 kinds of dead-end membranes, 0.4μm PE hollow fiber mem-brane has highest flux 225L/(h·m~3); In the 4 kinds cross-flow membrane component,1.2μm ceramic membrane has the highest flux 287L/(h·m~3). The main factors of dead-endtype and cross-flow membrane fouling rate were aeration and operating pressure.(2) In the membrane algae retention process, though the comparison of operationparameters such as membrane flux, energy consumption, membrane fouling rate etc. theoptimal dead-ended was 0.4μm PE hollow fiber membrane modules, the optimal operatingconditions: the pumping stop over = 4min: 1min, aeration = 1.2m~3/h, peristaltic pumpspeed = 160rpm. And the optimal cross-?ow membrane was 1.2μm ceramic membrane,the optimal operating conditions: the operating pressure = 0.04MPa, peristaltic pumpspeed = 300W.(3) The experimental results showed that the backwash: from 6min/120min adjustedto 3min/60min after 0.4μm PE hollow fiber membrane fouling rate decreased by 4.8%, 1.2μm ceramic membrane fouling rate decreases by 52.8%. 40kHz ultrasound effect onmembrane fouling rate orthogonal design the best dead-end membrane ultrasonic oper-ation for conditions on / off = 5min/5min, ultrasonic power = 300W. 0.4μm PE hollowfiber membrane fouling at low speed rate, high throughput and low power consumptioncharacteristics of membrane-based process to determine the optimal membrane.(4) Dynamic small scale hollow fiber membrane using 0.4μm PE retention algae,the algae retention rate was > 99%. Secondary sedimentation tank of algae comparedthe average length of stay longer process 314%. Device ef?uent SS, CODCr, TN,TPconcentrations were 4mg/L, 20mg/L, 13mg/L and 0.4mg/L, were to GB18918-2002 1-Aemission standards. After 14d of continuous operation, the membrane modules△TMPonly 0.01MPa.The experiment showed that, in algae bacteria symbiotic reactor using membranealgae retention process has high technical feasibility.