Assessment of the Application of Low-Cost MAP Precipitation Method for the Recovery of NH4+ from the Effluent of UASB Treating TFT-LCD Wastewater

• Main Authors: Jia-HuiWang, 王家慧
• Other Authors: Chih-Hua Chang
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/9kbkxy

碩士 === 國立成功大學 === 環境工程學系 === 104 === Optoelectronic semiconductor and high technology industries are growing in recent years in Taiwan. Among these industries, Thin Film Transistor Liquid Crystal Display (TFT-LCD) can be applied in many relative high technology products so it made the demand and output become higher and higher. As the output higher, the volume of wastewater becomes higher. The wastewater contains tetra-methyl-ammonium-hydroxide (TMAH), which processes with upflow anaerobic sludge blanket reactor (UASB). The TMAH transferred to ammonia then made the wastewater contains high concentration of NH4+. If the high concentration NH4+ of wastewater effluent to water body, it will cause irreversible impact. Therefore, TFT-LCD industries start to develop new technologies for reducing ammonia concentration. In this work, we evaluate the effectiveness and feasibility of applying a magnesium phosphate precipitation (MAP) method for further reducing the level of NH4+ by recovery of nitrogen from the effluent of UASB treating TFT-LCD wastewater, and generating struvite (MgNH4PO4‧6H2O) solids as slow-released fertilizer. Additionally, with an intention to cost down the MAP approach, source materials including magnesium from concentrated seawater brine, and phosphate recovered from the TFT-LCD manufacturing process, were applied in this study. First, the operational pH value and optimum molar ratio between ammonia from the UASB effluent, magnesium from the concentrated seawater brine and recovered phosphate, were determined to maximize the recovery rate of ammonia. Second, the cost of generating struvite from the proposed approach was evaluated. Third, the quality of generated struvite was assessed by analyzing the nutrient content, and the concentration of heavy metals in soils and vegetation when applying it as fertilizer. First, the highest median ammonia recovery rate of 89.78% (68.53% to 96.12%) was attained when the range of molar ratio (NH¬4+: PO43- : Mg2+) was adjusted to between 1: 1.0 : 1 to 1: 1.2: 1. The best pH value for synthesizing struvite solids using the proposed MAP approach is between 9.0 to 9.9. Second, the cost for generating 1 kg struvite solids (59% purity) is estimated to be 2 NTD/Kg-struvite by taking both the cost of adjusting pH value 44 NTD/Kg-struvite and purchasing concentrated seawater brine is 28 NTD/kg-struvite. The generated struvite solids (59% purity) consist of 4.5% nitrogen, 32.6% phosphorous, 1.8% potassium oxide and 32% organic matter. The concentration of Ni and Cu within the struvite solids exceed the limits of fertilizer standard in Taiwan. The heavy metal resource of Ni and Cu is from suspend solid in TFT-LCD wastewater. The original way to treat wastewater have to spend 14,260 NTD/Kg-struvite. The MAP precipitate method to treat wastewater have to spend 70 NTD/Kg-struvite. Therefore, the MAP precipitate method is cost effective. If the problem of heavy metal can be solve, it is feasible to apply to the nowadays society.