Characterization Of Biochar And Its Application In Yellow Water Treatment

With the rapid process of urbanization in China, the treatment of nitrogen and phosphorus in wastewater, and impoverishment of agricultural soils have become two serious problems. Collection of human urine, namely yellow water from source separation system and recycle of nutrients in yellow water might be a possible solution. Biochar, a porous material with nutrients adsorption capacity, is introduced into the system for treatment of wastewater, thus producing slow-release fertilizer for poor soil amendment. The system could relieve the burden of nitrogen and phosphorus treatment in wastewater, and at the same time improve soil fertility, leading to the sustainable development of environment and agriculture. In this thesis, basic properties of biochar produced at different conditions were analyzed, aiming at recycling of nutrients from yellow water. Based on the study, an adsorption process was developed with the combination of biochar and magnesium dosage, thus establishing an agricultural resource circulation system focusing on saturated biochar as slow-release fertilizer.The basic characteristics and nutrients adsorption capacity of biochar produced at different pyrolysis conditions from different feedstocks were studied. Biochar from agricultural residues possessed more hydrophilic and polar functional group and showed better ammonium nitrogen adsorption effects, with adsorption capacity of 8.8~10.1 mg/g, compared with 4.5~5.2 mg/g for biochar from wood chips and 5 mg/g for activated carbon. The pyrolysis temperature and duration time affected the adsorption ability of biochar. Pretreatment of magnesium loading process enhanced the recovery of phosphorus by biochar.Batch and columnexperiments were both conducted to optimize the recovery of nitrogen and phosphorus from yellow water through biochar adsorption. The adsorption mechanisms were analyzed as well. The combination of biochar and magnesium dosage enhanced s ynchronous recovery of both ammonium and phosphate. Recovery efficiency was affected by dosage amount, initial concentration of yellow water and process period. The adsorption process could be simulated by second-order kinetics and Freundlich adsorption isotherm, with the adsorption mechanisms of positive and negative ions combination, ion exchange, and crystallization and precipitation. The operation conditions of column experiments had a significant impact on biochar adsorption capacity. Generally, up-flow column filled by biochar mixed with Mg O, which run at low flow rate, showed better operation performance. A larger-scale column was operated continuously, ensuring low ammonium nitrogen concentration in the effluent. The final ammonium adsorption capacity of biochar reached more than 20 mg/g, higher than the results of continuous stirred tank reactor in batch tests.The impact of saturated biochar as slow-release fertilizer on agricultur al soil properties and crop growth was studied. Based on the results, the environmental and economic benefits of agricultural resource circulation system focusing on biochar were analyzed. The addition of slow-release fertilizer in soils enhanced the germination percentage, growth rate and harvest yields of two selected crops, with different effects for the two crops. Soil properties were improved at the same time, with increased p H and better fixation capacity for nutrients. In conclusion,the agricultural resource circulation system focusing on biochar has significant meaning for solid waste and wastewater treatment, resource recycle. The sustainable system possesses a bright future in China.