碳源添加方式对海水生物絮凝系统启动效率的影响

合理地添加碳源有利于生物絮凝系统的构建。为快速完成海水生物絮凝系统启动,在盐度为30的生物絮凝系统启动阶段探究了3种添加碳源(葡萄糖)方式对启动效率的影响。第一种在实验初始时一次性添加葡萄糖到生物絮凝系统中,使碳与总氮质量比达到15以上;第二种在系统运行的第1～10天,每天加入A组所添加葡萄糖总量的10%,此后若氨氮(TAN)上升至1 mg/L以上,则按照C/TAN为6来添加葡萄糖;第三种每天按照C/TAN为6来添加葡萄糖。结果显示:3个处理组的氨氮在实验期间总体上处于较低水平,亚硝酸氮和硝酸氮均有明显积累,但在系统运行第59天时降至最低水平。3组系统中絮体的胞外聚合物和粗蛋白等营养指标均呈现下降趋势。利用高通量测序技术对生物絮体的细菌群落结构进行分析,检测结果表明:3组生物絮体的主要优势菌群都属于变形菌门(Proteobacteria),持续添加碳源能够丰富生物絮凝系统中微生物种类。实验进行第55天时,3个处理组的生物絮凝系统启动完成。实验表明:在启动初始阶段以DOC/TN为15的比例添加葡萄糖及在系统运行期间按DOC/TAN为6的比例添加葡萄糖能够更好地形成生物絮凝系统。

Effect of carbohydrates addition methods on start-up efficiency of seawater biofloc technology system

Raising the carbon/nitrogen ratios of Biofloc technology(BFT) aquaculture system by providing carbohydrates can promote the growth of heterotrophic bacteria, and reform bioflocs with feces and lures in cultured water, so as to improve the utilization rate of feed protein and purify the aquaculture water. However, there is no uniform view on how to add carbohydrates. In order to prevent the aquaculture animals from being poisoned by ammonia nitrogen and nitrite nitrogen during the construction of BFT system, it is necessary to set the start-up stage of the BFT system. Therefore, a 60 days experiment was carried out to investigate three strategies of carbohydrates providing at the start-up stage of the biofloc system with salinity of 30 ppt, aiming at optimizing the adding strategy of glucose, so as to shorten the formation period of the biofloc system and stabilize the water quality quickly. The first method is to add glucose to the biofloc technology (BFT)system (group A) at a one-time to make the C/TN (total nitrogen) be 15(group A). The second is 10% total glucose of group A was added every day from 1st to 10th day, after that, if the total ammonia nitrogen (TAN) increased to above 1 mg/L, the glucose was added according to C/TAN of 6. The third is to add glucose every day according to C/TAN of 6. The results showed TAN in A and C treatment groups was generally at a low level during the experiment period. TAN in B group reached a peak value of (16.36±3.02)mg/L on the 31st days, nitrite nitrogen(NO₂^--N) and nitrate nitrogen(NO₃^--N) had a significant accumulation, but dropped to the lowest level on the 59th day. The three treatment groups both had assimilation and nitrification, but the nitrification was obviously inhibited in the system with continuous addition of carbohydrates. The extracellular polymeric substances (EPS) and crude protein of bioflcos in the three treatment groups showed the trend of decreasing during the experiment period, and the settling velocity of bioflocs of the three treatment groups becomes better. The bacterial community of bioflocs was analyzed by high-throughput sequencing. The results showed that, at the phylum level the main dominant microflora of the 3 different groups were Proteobacteria. Besides,Bacteroidetes and Planctomycetes were also found in group C. At the class level, the main advantage microflora in group A and group B were mainly Gammaproteobacteria, while the main dominant microflora in group C are Gammaproteobacteria,Alphaproteobacteria, Flavobacteria and Phycisphaerae. Thus, continuous addition of carbon sources can enrich microbial species. The experiment shows that the three carbohydrates additions can stabilize the water quality in about 55 days in a seawater aquaculture system using bioflocs technology.It can be concluded that the best method for the start-up of seawater BFT system is maintaining C/N 15 initially, then adding carbon source to 6 of C/N when TAN was up to 1 mg/L.