Nitrogen And Phosphorus Removal From Livestock And Fowl Breeding Wastewater In Phragmites Australis And Alpinia Aquatica Constructed Wetlands

The pollutants from the livestock production are becoming the third source of pollution after industrial wastes and domestic garbage. The contaminants are composed of harmful gases from animal body, excreta, scraps and feathers, as well as the washing water from the livestock production factories. A majority of organics, suspended substance and ammonia nitrogen are removed after primary and secondary treatment, but it needs the subsequent treatment such as constructed wetlands to achieve required effluent standard. Phragmites australis. Trin. and Alpinia aquatica(Koen.) Rosc. which has not to be used in constructed wetland treatment. To study the nitrogen and phosphorus removal from livestock and fowl wastewater. Two wetland systems were established. One simulated wetland used soils, river sands and gravels, and in it different plants were arranged in groups. Another system is pilot-plant, which has being operated more than one year. The results are summarized in the following:(1) Wetland with plants were superior to unplanted in nitrogen and phosphorus's removal. Variance analysis showed that there was no significant difference among the different treatment, which means that the plants removal was not the key factors. And the complex plants-bed can remove more nitrogen and phosphorus than the only one plant-bed.(2) The C/N can also had an influence on the removal efficiency. In Phragmites australis bed, Alpinia aquatica bed and complex bed, NH₄⁺-N had the best removal effect at 1:1, 3:1, 4:1 respectively. When FeCl₃ was added in the substrates, the removal efficiency of TP increased with the increase of FeCl₃. When 0.0025g FeCl₃ was added to per gram substrate, the effect of nitrogen and phosphorus removal is the best.(3) The ability of nitrification was the weakest, and denitrilfication intensity was the highest in the 1/3 position of treatment bed of the constructed wetlands system. Velocity of nitrification and denitrification were both the fastest during the first 8h. Intensity of nitrification and denitrification obviously had a phenomenon of stratification. The upper layer is better than the lower layer. And there was a negative correlation between the nitrification and denitrification rate. Denitrification intensity varied with different values of C/N in the study, and it could reach the maximum while C/N was 3. Through 6 months' water quality monitoring, the pollutants degraded along with the bed length. And the degradation varied with time and positions. As for NH₄⁺-N, the best removal time is in August, and best removal site is the front part. And for TP, the best removal time is in July, and best removal site is the aftering half part.(4) The adsorption of phosphorus in the soil increased with the increase of oscillating time. Eight hours were the optimal oscillating time for sand and gravel's adsorption. The adsorption of phosphorus in the substrates do fit with the Langmuir. Freundlich and Temkin equations. Nevertheless the Langmuir equation was the optimum. There exists on competition adsorption among the three mixed substrates.(5) The constructed wetland removes the phosphorus mainly by the adsorption of substrates. The adsorptive capacity was the soil>sand>gravel. In the constructed wetlands of sewage treatment plant, substrate adsorption to phosphorus increased along with the bed length. When the plants were applied to treat the waste water, the distribution of nitrogen and phosphorus was different in the root, stem and leaf. The roots of Alpinia aquatica have best nitrogen adsorption ability than other parts, and the aerial part of Phragmites australis have better nitrogen adsorption ability. Phosphorus removal ability of Alpinia aquatica was not good, especially in the simulated constructed wetlands. But the leaves of reed could efficiently remove phosphorus. The content of nitrogen and phosphorus reduced with the bed length.