| Prevention of water eutrophication and cyanobacteria bloom has become an urgent task of water pollution control and ecological restoration. Regular designated salvage by rescue vessel was an effective way to reduce cyanobacteria pollution and its outbreak again in Taihu, Dianchi and other places where the cyanobacteria break out frequently. Cyanobacteria contained much protein, nitrogen, phosphorus and other nutrients. Composting with cyanobacteria was a major way to deal with salvaged cyanobacteria and produce high quality organic fertilizer, which can not only free cyanobacteria salvage work from any worries, but also make the using of cyanobacteria become a new environmental protection industry. As a special material of compost, the cyanobacteria contained a large number of microcystins (MC), which remained largely in fertilizer after inappropriate composting. Application of cyanobacteria composting to land would influence the crop growth and increase the risk of human health. To optimize the technological parameters of the aerobic composting of cyanobacteria, nearly three years of laboratory and pilot test were conducted. A harmless treatment technique was established to aim at aerobic composting of salvaged cyanobacteria, after repetition, verification and improvement based on experimental data.1. Rice husk, wheat bran, pot ale and tar were used as packing materials when composting with cyanobacteria. Results showed that carbon and nitrogen contents decreased23.2%～36.2%and40.7%～56.9%, respectively at the end of composting. Contents of total phosphorus, total potassium and ash were increased during the composting. The total nutrient content (i.e. N+P2O5+K2O) could meet the standard of organic fertilizer. The germination index in all treatments was more than80%at the end of composting of cyanobacteria. The content of MC lowered100ug/kg after composting of30days; while MC-RR lowered the limit of detection of10ug/kg at the end of composting. Compared with MC-RR, the degradation rate of MC-LR was more than90%in all treatments. The compost effect was best in treatment with wheat bran. The contents of MC-RR and MC-LR were significantly correlative. MC content was positively correlative with organic carbon and total nitrogen and negatively correlative with total phosphorus, total potassium, total nutrient content and gray content. 2. Different water content influenced the composting process of cyanobacteria. Results showed that pH and nutrient contents were not significantly different between55%,65%and75%moisture treatments. Nitrogen loss was higher in55%moisture treatments than those in65%and75%moisture treatments. However,55%moisture was benefit to composting mature and germination index. The total nutrient content (i.e. N+P2O5+K2O) and organic matter contents were5.12%,4.90%and4.56%,34.64%,37.70%and38.80%, respectively, in three moisture treatments, which could meet the standard of organic fertilizer. The content of microcystins was lowest in55%moisture treatments.3. Ratio of carbon to nitrogen (C/N ratio) was the major factor to influence composting effect and secure utilization of cyanobacteria. C/N ratio of5,15and25were conducted to analyze the composting speed and the degradation of MC in dewatering cyanobacteria. Results showed that the physical and chemical characteristics were significantly (p＜0.05) different between treatments. The composting speed was significantly faster in treatments of15and25C/N ratio compared with treatment of5C/N ratio. However, nitrogen loss was larger in the previous two treatments, i.e.,25＞15＞5C/N ratio. Total nutrient contents of all treatments enhanced at the end of composting, in which only25C/N ratio treatment met the requirement of the national industry standard of organic fertilizer. The degradation rates of MC-LR (L indicated leucine) were55.48%,80.27%and65.39%, respectively in each treatment; while the degradation rates of MC-RR (R indicated arginine) were99.21%,97.15%and95.97%, respectively. The degradation rate in15C/N ratio treatment was higher than other treatments.4. Nitrogen protecting agent played a significant effect on inhibiting nitrogen loss during the composting of cyanobacteria. Compared with composting of cyanobacteria by itself (control treatment), addition of ordinary superphosphate and vinegar residue could reduce32.72%and7.65%nitrogen loss during the composting. The treatment adding with ordinary superphosphate was much better than treatments of vinegar residue addition and control. No significant effect on nitrogen loss inhibition was found between treatment with vinegar residue addition and control treatment.This study has proposed the optimal technique and parameters for practicle composting of dewatering cyanobacteria. Meanwhile, the residue of MC-LR and MC-RR can not exceed30ug/kg (dry weight) and15ug/kg (dry weight), respectively, after completely composting of dewatering cyanobacteria. These results would provide theoretical principle for establishment of standard models and operating rules for high temperature composting technology of cynaobacteria. |
PDF Full Text Request