Improvement of full-scale activated sludge for treating industrial metal-containing organic wastewater by using the equilibrium stoichiometry

• Main Authors: Jhong-syun Yu, 余忠勳
• Other Authors: Wei-Hsiang Chen
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/ab99g9

碩士 === 國立中山大學 === 環境工程研究所 === 103 === Wastewater treatment technologies can be divided into chemical, physical, and biological methods, as the biological approaches are commonly used. The biological processes treat wastewater by removing organic and inorganic contaminants in water through metabolism of microorganisms. The advantages of biological treatment technologies include lower processing costs, higher treatment efficiencies, easy operations, minimal impact of secondary pollutions. In the last decades, the industrial wastewater treatment technologies have become the focus of attention, notably when illegal wastewater discharges have been frequently reported. Given that industrial wastewaters typically contain hazardous substances such as heavy metal, the improper treatment and discharges of industrial wastewaters are likely to cause serious environmental pollutions. In this study, a fabless semiconductor processing plant that generates multiple wastewaters was selected for investigation and optimization. Furthermore, chemical and microbial stoichiometry and the associated mechanism theories were applied to analyze the activated sludge and to predict the effects of different nutrient source strategies on the treatment performances and costs. The source wastewaters contain a municipal wastewater, a wastewater containing a high concentration of isopropyl, and heavy metal-containing industrial wastewater. The municipal and industrial wastewaters were treated by two separate secondary treatment processes, while the isopropanol solution was treated by outsourcing. As a result, the challenges of this study are: (1) high concentrations of heavy metals in wastewater inhibited the performance of activated sludge; (2) the nutrients in the industrial water was insufficient to support the activated sludge; (3) the isopropyl waste solution was treated by outsourcing, increasing the treatment costs. This study includes four stages of results and discussion. In the first stage, the wastewater treatment plant was investigated to fully understand the current situations regarding the operations, discharges, and treatment performances. The water quality was regularly monitored, as the parameters of concern included the pH, mixed liquor suspended solid (MLSS), and dissolved oxygen. The chemical oxygen demand (COD) and copper concentrations of the treated water, and treatment efficiency were 50 mg/L, 30-50 mg/L as Cu, and 10%-20%. Next, the two existing secondary treatment processes were combined to simultaneously treat the municipal wastewater and heavy metal-containing industrial wastewater. The municipal wastewater was used to dilute the heavy metal concentrations in the industrial wastewater and the isopropanol solution was also added for treatment and used as a carbon source of the activated sludge. In the third stage, the treatment processes were modified and the treated water quality was monitored regularly. The COD in the treated water ranged from 20 to 50 mg/L, and the treatment efficiencies of COD, Cu, and nickel (Ni) ranged from 80 to 95%, from 94 to 98%, and from 70 to 95%, respectively. The ammonia concentration ranged from 30 to 35 mg/L as N. In the fourth stage, the concepts and theories of chemical and microbial stoichiometry were applied. Given the COD concentration, nitrogen and oxygen consumption rates controlled within the range of 130 to 260 mg/L, 4.66 to 9.33 kg/d, 115.04 to 648.56 kg/d, respectively, the sludge retention time (θx) was 3.2 d; the residence time (θ) was 6.2 hours; the microbial decay rate was 0.15 d-1; the half-velocity constant (K) was 10 mg acetate/L; the biodegradable fraction of the sludge (fd) was 0.8; the cell yield coefficient rate (Y) was 0.361 g cell/g isopropanol; the substrate consumption rate (q) was 1.706 g isopropanol/g cell-day. The full reaction that treats isopropanol in the activated sludge was: 0.056 (CH3)2COH- + 0.214 O2 + 0.007 NH4+ → 0.083 CO2+ 0.05 HCO3-+ 0.022 C5H7O2N + 0.16 H2O, giving an isopropanol consumption rate of 235.98 kg/d, an oxygen consumption rate of 482.8 kg/d, microbial growth yield of 172.92 kg/d, and a nitrogen demand of 6.91 kg/d. If acetic acid was treated, the full reaction became: 0.125 CH3COO-+0.215 O2 +0.007 NH4+ → 0.097 CO2 + 0.12 H2O + 0.222 C5H7O2N + 0.12 HCO3-, giving an acetic consumption rate of 235.98 kg acetate/d, an oxygen consumption rate of 220.2 kg/d, a microbial growth rate of 80.6 kg/d, and a nitrogen demand of 3.13 kg/d. This study effectively improved the full-scale wastewater treatment processes with the steps including the water quality monitoring, nutrient selection and substitution, system modification, full-scale application, and final treatment performance demonstration, providing insights into the mechanisms and possible strategies for other wastewater treatment plants to face the similar aerobic wastewater treatment challenges.