Applied Research On Macrophyte Fermented Broth In Denitrification

Carbon sources is the electron donor in the process of denitrification, as well as the main source of energy needed for microbial growth and reproduction. A common problem is the shortage of denitrification carbon source in the process of high nitrogen and low carbon wastewater treatment, thus, the main solution to strengthen denitrification effect is via adding external carbon sources. Traditional carbon sources (mainly including low molecular organic substances as methanol, acetic acid and sugars as glucose) are easily biodegradable, but there are drawbacks such as high cost, inconvenient transportation and easy jam. New-type carbon sources represented by fiber materials and some biodegradable artificial materials are cheap and accessible. They also have a good performance in improving denitrification effect. However, this kind of solid carbon source can only be applied to constructed wetland system and they could not be used as added carbon source in the traditional wastewater treatment technology. Besides, these materials have poor controllability of carbon source release and long hydraulic retention time. In recent years, it is reported that the denitrification effect of a large amount of short chain volatile fatty acids (VFAs) as acetic acid, propionic acid was better than methanol, acetic acid and other traditional single carbon source, and the VFAs have been found in anaerobic fermentation product which derive from urban organic wastewater (such as brewery wastewater, molasses wastewater, starch wastewater, etc.) and city sewage plant sludge.In this paper, the macrophytes from constructed wetland were used as raw materials for producing acid under anaerobic fermentation condition to investigate the feasibility of their fermentation liquor as additional carbon source in denitrification. Firstly, the releasing regularity of nitrogen, phosphorus, and carbon of plant body were studied under different types of wetland vegetation (emergent plants and submerged plant), fermentation temperature (10℃,25℃ and 37℃) and pretreatment method (crushing and no pretreatment), as well as the effect of these factors on the VFAs production, the producing rate and the type of acid. The results indicated that the release amount order of nitrogen of macrophytes was Thalia dealbata> Potamogeton crispus> Vallisneria spiralls>, and the release amount order of phosphorus was Vallisneria spiralls> Thalia dealbata> Potamogeton crispus> Typha orientalis presl. And the release amount orders of carbon and total VFAs were Potamogeton crispus> Vallisneria spiralls> Thalia dealbata> Typha orientalis presl; plant type have little influence on acid type and acetic acid is the main product in the fermented liquids of four plants, followed by butyric acid and propionic acid, and formic acid yield is relatively low; compared to emergent plants, submerged plants were more suitable as the substrate for fermentation to produce acid. Under different fermentation temperature, the order of nitrogen, carbon release amount and release rate was 37℃> 25 ℃> 10℃, the acid yield and rate of acid production were also show the same laws; by contrast, fermentation temperature had less influence on the release quantity and release rate of phosphorus, the release rates of phosphorus were all rapid under three temperatures. Pretreatments had very significant effect on the release rates and release amount of nitrogen, phosphorus, carbon and the acid produced (p<0.01). The release rates and release amount of nitrogen, phosphorus, carbon and VFAs produced from crushing plant were significantly higher than that produced from unpretreated plant.The simulated anaerobic contact reactor and horizontal subsurface flow constructed wetland system were constructed in our lab in order to investigate the strengthened denitrification effect of P.crispus fermentation liquor as external carbon source on the common wastewater treatment process and sewage plant of tail water depth treatment technology. The results showed that P.crispus fermentation liquor could significantly improve denitrification effect of both technologies. Under COD/N=16, HRT=4h, the removal rates of TN were increased from 5.3%,4.3% (without external carbon source) to 84.0%,79.6% under simulated anaerobic contact reactor and horizontal subsurface flow constructed wetland system, respectively, and the removal rates of NO3--N were increased from 12.0%,4.9% to 98.7%,100%; the optimum inflow COD/N were both16:1, and the optimum HRT were 4-8h and4h, respectively.