| In order to reclaim the treated municipal wastewater as high quality recharge sourcesof urban river, the total nitrogen (TN) in effluent of municipal wastewater treatment plantwas strictly limited according to the discharge standard. The processes of tertiary nitrogenremoval respectively using sodium acetate, polycaprolactone (PCL),polyhydroxyalkanoate (PHA) and hydrogen as electron donors were investigated in thispaper. An innovative dual media filter with solid carbon pellet and sand, as well as a novelhydrogenotrophic denitrification bioreactor with bubble-less hydrogen supplying weredeveloped for the tertiary nitrogen removal of municipal secondary effluent. Thecharacteristics of microbial community structure in the denitrifying bioreactors withdifferent electron donors were investigated. The main conclusions were as follow:(1) The denitrifying biofilter with sodium acetate as electron donor could be faststarted up in5days. When the operating temperature was below10oC, the TNconcentration in effluent was below3.0mg/L consistently in a long-term, correspondingdenitrification rate was2.81kgN/(m3·d). The optimal ratio of COD/N in influent rangedfrom4.4to4.8, in order to keep the performance of nitrogen removal well and controlthe organic residue in effluent.(2) The dual media filter with solid carbon material and sand was developed for thetertiary nitrogen removal from municipal wastewater. In this study, PCL and PHA werepacked in the filters respectively. The nitrate nitrogen and suspended solid (SS) wereremoved simultaneously in the dual media filters. The TN concentration in effluent wereboth below10.0mg/L at18~20oC, corresponding denitrification rates were3.74and0.51kgN/(m3·d) for the filters with PCL and PHA respectively. When the temperature droppedto8~9oC, the denitrification rates dropped to1.42and0.13kgN/(m3·d), meanwhile thenitrite were accumulated in both of the effluents with the concentration of1.2and2.7respectively. When the concentration of SS in influent were from16.0to19.0mg/L, theconcentrations of SS in effluent were both below4.0mg/L. The concentrations of totalorganic carbon (TOC) increased by0.63and0.57in effluent respectively.(3) The hydrogenotrophic denitrification process for tertiary nitrogen removal frommunicipal wastewater was developed with bubble-less hydrogen supplying and performed steady and efficiently in a long-term. The TN concentration in effluent wasbelow1.0mg/L consistently at30oC. When the temperature drop to15oC, the TNconcentration in effluent increased to3.0mg/L, corresponding denitrification rate was0.23kgN/(m3·d). The TOC concentration in effluent increased by0.41mg/L on average.The impact of dissolved oxygen (DO) on denitrification was not obvious. The DOconcentration in effluent only decreased1.20mg/L on average.(4) The microbial community diversity in tertiary denitrification unit was lowerthan that in activated sludge from biology treatment unit. The influence of electron donoron microbial community structure was obvious. The dominant bacteria were significantlydifferent in each bioreactor. The bacteria belonging to four genuses of Proteiniphilum,Dysgonomonas, Silanimonas and Arenimona, which were not reported ashydrogenotrophic denitrifying bacteria, were observed to abound in the hydrogenotrophicdenitrification system.(5) The order of costs of tertiary nitrogen removal from municipal wastewater,when only take the cost of electron donor in account, was methanol, hydrogen, actatePHA and PCL, corresponding with the cost of6.96,11.15,12.04,68.4and95.2CNY/kgN. |
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