Optimization And Mechanism Of Algae-laden Water Treatment

Water pollution caused by the excessive growth of blue-green algae has become a growing environmental problem. One current approach to reducing the algae in Taihu Lake is to refloat the algae after a bloom has occurred. It can remove nitrogen and phosphorus in the lake simultaneously. Algae-landen water which contains around 99% water needs timely and effective treatment. To achieve the target of reduction, recycling, harmless treating of algae-laden water, the paper focuses on using recycled material source, designing reactors for algae-laden water and exploring its gas production mechanism. And the paper studys the treatment of the anaerobically digested effluent. The main results are as follows:Blue algae anaerobic fermentation characteristics of composted time showed that soluble organic matter in blue algae (proteins and polysaccharides) transfers from solid to liquid during the decomposition process, so that appropriate decomposition of blue algae accelerates the gas production. Biogas production potential was 248.1mLCH4/gVS in the system of composted 7d blue algae. At initial stage of fermentation, proteinase and coenzyme F420 activity tended to increase with increasing composted time; TTC-dehydrogenase activity was the highest in the system of composted 7d blue algae.The effect of stirring intensity was the main factor on blue algae anaerobic fermentation for biogas production, and stirring duration was the minor one. Excessive stirring intensity and frequency could destroy the fitness for anaerobic microbial growth, so that the synergy between different anaerobic microorganism species in the system would be destructed partially, leading to an activity decline of the protease, dehydrogenase, and coenzyme F420 in the sludge and reduction of gas production rate. Otherwise, low stirring intensity and prolonged stirring cycle could make blue algae easy to float, resulting in less effective contact in microorganisms in the sludge and then lower cyanobacteria conversion efficiency. The optimal stirring factor for blue algae anaerobic fermentation gas production was determined by the statutory response surface as stirring cycle of 6 h, stirring duration of 20 min/per time, and stirring intensity of 56 r/min.According to the characteristics of algae-laden water, up-flow anaerobic sludge blanket (UASB) reactor and anaerobic bafflted reactor (ABR) were improved by adding agitation devices and elastic filler, respectively. The results showed that under the following conditions of dosing seed sludge, continuous operation with improving the load by steps, after 35 days the algae-laden water could be successfully processed. The study found that the intermittent stirring device and the reflux system could overcome the drawbacks of blue algae floating and crusting in the reactor and at the same time accelerate the mass transfer in the improved external circulation UASB. After the successful launch of the improved external circulation UASB, the granular sludge was found in the stabilization stage with coupled growing micro-organisms such as filamentous bacteria, rod-shaped bacteria, and spherical bacteria.The soft filler played a key role in treating blue algae successfully by the improved ABR. It was found that the soft filler had function on forming biofilm and training granular sludge in the reactor. In addition, it was benefit to promote the more reasonable space distribution of the microbial communities in the compartments. Protease content of granular sludge in ABR decrease and coenzyme F420 content increased progressively along separation chambers. It was consistent with the quantity of archaea and bacteria along separation chambers in the reactor.On the basis of the successful launch, the improved external circulation UASB and the improved ABR reactor have good processing performance. During the start-up and the stable operation period of the improved external circulation UASB, the dominant populations of archaea in granular sludge changed. Archaea were found apparent niche separation during methanogenic phase. After stable operation of the improved external circulation UASB, the main parts of Archaea were methanogenic bacteria, including:Methanolinea, Thermogymnomonas, Methanoregula, Methanobacterium, Methanosaeta, Methanoculleus.The improved ABR has obvious characteristic of phase separation. Microbial communities could achieve a new equilibrium through its own ability to adapt regulation in the improved ABR. After stable operation of the improved ABR, the main parts of Archaea were methanogenic bacteria, including:Methanoregula, Methanobacteriaceae, Methanosaeta, Methanoculleu and Thermogymnomonas.The results showed that the anaerobically digested effluent algae-laden water was treated by combined process of contact oxidation and aquatic vegetable wetland. The average effluent of the combined process all achieved the first standard of GB18918-2002. The contact oxidation tank reduced the inlet load of the subsequent aquatic vegetables wetland. Observing by scanning electron microscope (SEM), it was found that ipomoea aquatica roots had huge surface area for the enrichment of microorganisms and the interception of organic matters. Gas chromatography-mass spectrometer (GC-MS) analysis results demonstrated that organic pollutants of the slurry could be removed effectively during the combined process, and biochemical treatment of the contact oxidation tank had a good performance in dealing with alkane pollutants, aromatic hydrocarbons and heterocyclicthe compounds. The microcystins could be removed effectively by the combined process. The synergistic degradation of the enriched microbes in contact oxidation and aquatic vegetable wetland was the main reason for microcystins removal.The study found that cabbage production, which was fertilized by low concentration fertilizer of the anaerobically digested effluent of algae-laden water, increased 24% compared with the control group. Compard with chemical fertilizer, the soluble sugar content of cabbage increase, the vitamin C content decrease. In order to ensure food safety, cabbage must be watered with low concentration fertilizer with appropriate irrigation slurry and water ratio of 1:2. Meanwhile, compared with the control group, slurry fertilizer of algae-laden water could effectively improve the physicochemical property of soil and increase the content of organic matters as well as the entire nitrogen in soil.