以丝瓜络为碳源的固相反硝化系统性能研究

【目的】构建以丝瓜络为碳源的固相反硝化系统，并探究在不同水力停留时间（hydraulic retention time, HRT）和进水硝酸盐浓度（Influent nitrate concentration, INC）下该系统的反硝化性能，为丝瓜络作为反硝化碳源在水产养殖尾水处理工艺的进一步优化提供理论依据。【方法】以丝瓜络（loofah sponge, LS）为一维反硝化反应器（denitrification reactor, DR）外加碳源，在流场环境下，测定不同HRT（16、20、24和28 h）和INC（50、75、100和125 mg/L）下反硝化系统对硝酸盐氮（NO3?-N）、亚硝酸盐氮（NO2?-N）、氨氮（NH4+-N）、总氮（TN）、总磷（TP）和COD的去除效果。并采用基于Illumina Miseq测序平台的高通量测序技术，对丝瓜络反硝化反应器（LS-DR）在运行初期和末期时的细菌群落结构进行分析。【结果】当INC为50 mg/L，HRT为24 h时，LS-DR的NO3?-N去除率和TN去除率均达到最大，分别为98.97±0.52%和97.84±0.94%，同时出水NO2?-N浓度也达到较低水平（小于0.5 mg/L）；在HRT为24 h的基础上，当INC延长至75、100和125 mg/L时，其NO3?-N去除率和NO3?-N去除速率（nitrate removal rate, NRR）均随INC的增加而显著增加（P < 0.05），出水COD则随INC的增加而降低，但均未实现完全反硝化，然而，LS-DR在整个实验期间均能完全去除NH4+-N；扫描电镜结果显示丝瓜络表面结构有利于微生物附着生长；高通量测序结果显示LS-DR的优势菌门包括变形菌门（Proteobacteria）、拟杆菌门（Bacteroidetes）、弯曲杆菌门（Campilobacterota）、厚壁菌门（Firmicutes）和疣微菌门（Verrucomicrobiota）；被鉴定的优势菌属中热单胞菌属 (Thermomonas, 1.46%)、陶厄氏菌属 (Thauera, 0.55%)、固氮螺菌属 (Azospira, 3.32%)、Simplicispira（1.01%）、假黄色单胞菌属 (Pseudoxanthomonas, 0.39%)、草螺菌属 (Herbaspirillum, 3.02%)和Uliginosibacterium（0.9%）能够促进反硝化的进行，Cytophaga xylanolytica（1.61%）和Cloacibacterium（2.69%）主要参与了丝瓜络的降解，黄杆菌属 (Flavobacterium, 1.17%)和Diaphorobacter（0.64%）既能进行反硝化，也能降解丝瓜络。【结论】LS-DR的最佳HRT为24 h，最适宜的INC为50 mg/L。【意义】本研究为丝瓜络固相反硝化工艺的优化提供了理论基础，为开发应用新型缓释碳源提供参考。

Study on solid phase denitrification performance system using loofah sponge as carbon source

The second national pollution sources survey showed that the total nitrogen emission from aquaculture is 99100 tons in 2017. To protect the environment and human health, it is important to remove nitrogen from aquaculture wastewater before discharged to surrounding waters. Biological denitrification is considered the most promising approach methods, since nitrate can be reduced to harmless nitrogen gas by bacteria. Sufficient carbon source is necessary during heterotrophic denitrification process. To solve the problems mentioned above, external carbon sources such as methanol, acetic acid and glucose were added to the wastewater, whereas they were generally high-cost, high-energy and high operating requirement. In contrast, agricultural wastes were used as carbon source, which has shown significant economic advantages and high-efficiency. Many aquaculture wastewater treatment systems often face variations in hydraulic retention time (HRT) and Influent nitrate concentration (INC) which are caused by acute change of wastewater characteristics and production, and HRT and INC often exert a profound effect on the treatment performance of biological treatment systems. The purpose of this study is to construct a solid-phase denitrification system with loofah sponge as carbon source, and investigate the effects of HRT and INC on the denitrification performance of loofah sponge-denitrification reactor (LS-DR), so as to provide a theoretical basis for the further optimization of denitrification process of loofah sponge as denitrification carbon source in aquaculture tailwater. Loofah sponge, one typical agricultural waste, are studied as the carbon source for solid phase denitrification under dynamic flow conditions by using 1-D column experiment. We aim to preliminarily investigate the LS-DR’s NO3?-N, NO2?-N, NH4+-N, TN, TP and COD removal effect under different HRT (16, 20, 24 and 28 h) and INC (50, 75, 100 and 125 mg/L). The optimal HRT of denitrification reactor were optimized by one-way ANOVA analysis. And, the high-throughput sequencing technology based on Illumina MiSeq platform was used to analyze the bacterial community structure of LS-DR in the initial and final stages of operation. The results indicated that when INC=50 mg/L and HRT=24 h, the removal efficiency of both NO3?-N and TN in LS-DR reached the highest value, which were 98.97±0.52% and 97.84±0.94% respectively. And NO2?-N was also at a low level (< 0.5 mg/L). On the basis of HRT of 24 h, when INC increases to 75, 100 and 125 mg/L, the nitrate removal efficiency and nitrate removal rate (NRR) of LS-DR increased significantly with the increase of INC (P< 0.05), and the effluent COD decreased with the increase of INC, but LS-DR did not realize complete denitrification. It is worth noting that LS-DR can completely remove NH4+-N throughout the experiment. After 14 days of operation, SEM results showed that the surface structure of LS was conducive to the attachment and growth of microorganisms; High throughput sequencing results showed that the dominant bacteria of LS-DR included Proteobacteria, Bacteroidetes, Campilobacterota, Firmicutes and Verrucomicrobiota. Among the identified bacteria, Thermomonas (1.46%), Thauera (0.55%), Azospira (3.32%), Simplicispira (1.01%), Pseudoxanthomonas (0.39%), Herbaspirillum (3.02%) and Uliginosibacterium (0.9%) can carry out denitrification. Cyphaga xylanolytica (1.61%) and Cloacibacterium (2.69%) are mainly involved in the degradation of towel gourd, Flavobacterium (1.17%) and Diaphorobacter (0.64%) can both denitrify and degrade LS. According to the analysis of the above results, it is considered that the optimal HRT of LS-DR is 24 h and the optimal INC is 50 mg/L. This study provides a reference for the optimization of loofah sponge solid-phase denitrification process and promotes the development and application of new slow-release carbon sources.