| 摘要: | 本論文係針對熱處理業中所產生的高油脂、高懸浮固體、高有機物廢水，評估最適當的處理程序。主要研究目的包括：(1)廢水水質特性的探討，(2)評估以化學混凝法去除廢水化學需要量(COD)條件，(3)探討以多孔性擔體生物膜處理程序(添加基質系統及未添加基質系統)進行化學混凝後廢水之三級處理的操作效能。
研究結果發現金屬熱處理業製程中的三股廢水，包括：淬火處理程序廢水(COD 1.45×105 mg/L, SS 74.33g/L)、表面精密研磨處理程序廢水(COD 4.0×105 mg/L, SS 17.665g/L)及廢油氣水洗處理程序廢水(COD 2.5×104 mg/L, SS 9.34g/L)，都具有高 COD 及高懸浮固體物(SS)之性質。化學混凝方法評估結果顯示，廢油氣水洗處理程序廢水以添加PAC的混凝效果最佳(pH7.2, PAC200mg/L)；淬火處理程序廢水以添加Na2S/PAC的混凝效果最好(pH10.4, Na2S/PAC 200mg/L/300mg/L或Na2S/PAC 300mg/L/300mg/L)；而表面精密研磨處理程序廢水則只能以添加PSAW混合型混凝劑才具有混凝效果(pH7.2, PSAW 30000 mg/L)。經化學混凝處理後的混合廢水所含COD物質均屬於有機碳化合物(TOC/COD＝0.25)，但BOD5佔廢水有機碳之比例極低(BOD5/TOC＝0.06、BOD5/COD＝0.01)，與生物可分解性廢水之性質相差甚大，因此可判定混凝後廢水中之有機碳大多屬於不易生物分解性或生物難以分解性的有機物。
由多孔性擔體生物膜程序之MLSS測量及擔體生物膜生長觀察的結果顯示，添加基質系統因外部基質溶液添加，提供了微生物在反應槽內持續存在及增殖的基本要素，由於微生物能持續生長，對進流廢水COD濃度表現出明顯的(p＜0.05)降解效率(各試程平均值範圍32~60%)，相當於進流廢水COD濃度可減少125~231 mg/L (各試程平均降解範圍)。反觀，無添加基質系統反應槽中，進流廢水COD無法提供微生物生長，生物膜無法形成，因此對進流廢水COD無降解能力。在外部基質的添加下生物處理程序若延長HRT對進流廢水COD的降解有明顯的幫助。尤其HRT操作16小時(試程六)，添加基質系統之出流水COD雖然為151±31 mg/L，但是其SCOD僅為90±21 mg/L，此差異可能為生物處理後出流水中所帶出的SS(大多為微生物菌體)貢獻COD所致。因此，建議於生物程序後再加入一個砂濾池或表面下流動式人工溼地(subsurface flow constructed wetland)去除SS，最後的出流水應可符合SS(＜30 mg/L)及COD(＜100 mg/L)的放流水標準要求。建議可將化學混凝處理後廢水與廠區生活污水稀釋混合處理以降低進流生物膜程序之COD濃度並取代部分的基質添加，以降低操作成本。
This thesis investigated the appropriate processes for treating the wastewater with high contents of fat, suspended solid and organic matter, which was generated from a heat-treating industry. The main aims of the study included: (1) examine the characteristics of wastewater from the industry, (2) evaluate the suitable coagulation methods as secondary treatment for removing chemical oxygen demand (COD) from wastewater, (3) investigate the feasibility of a porous carrier bio-film process used as advanced treatment with and without external addition of organic nutrient so as to remove the residue COD to meet the Effluent Standard.
The wastewater in a heat-treating industry normally produced from the quenching process, precise surface pulverizing process, and oil-gas scrubbing process. Wastewater analysis results showed that the stream from quenching process contained around 1.45×105 mg/L of chemical oxygen demand (COD) and 74.33 g/L of suspended solid (SS). Wastewater from the precise surface pulverizing process averaged 4.0×105 mg/L of COD and 17.665 g/L of SS, while wastewater from the oil-gas scrubbing process averaged 2.5×104 mg/L of COD and 9.34 g/L of SS.
The evaluation of chemical treatment of wastewater was conducted by a series of Jar test using PAC (Polyalumium chloride), Na2S(sodium sulfide)/PAC, or PSAW as coagulants. COD reduction from oil-gas scrubbing process wastewater was most effective (98~99%) by using PAC alone (pH7.2, PAC 200mg/L), whereas use of Na2S/PAC (pH10.4,
Na2S/PAC 200mg/L/300mg/L or Na2S/PAC 300mg/L/300mg/L) was the most efficient method for COD reduction from quenching process wastewater (95~99%). COD in pulverizing process wastewater could be considerably reduced by 58~93% only using PSAW (pH7.2, PSAW 30000 mg/L) as coagulant. After chemical coagulating treatment, the residual COD of wastewater was found to be organic origin (TOC/COD＝0.25), but such organic matters were belonged to non-biodegradable or not easily biodegradable compounds because their low BOD5 content (BOD5/TOC＝0.06、BOD5/COD＝0.01).
Additionally, two porous carrier bio-film reactors in bench-scale were employed to receive the wastewater pretreated by coagulation process mentioned above. Besides the continuous feed of influent wastewater, external organic nutrient liquid was additionally supplied to one reactor (so called as substrate added system), whereas only tap-water, under the same flow rate as the former, was supplied to another reactor (so called as substrate nonadded system). A denser bio-film occurred on/in the porous carrier and a higher concentration of mixed liquor suspended solids (MLSS) were both observed in the substrate added system than substrate non-added system. This implies that external organic nutrient did provide substrates available for microbial growth in reactor. This result led to an effective reduction of COD from the influent wastewater (32~60% or a decrease of 125~231 mg/L, p<0.05) that was occurred in substrate added system. Conversely, there was no significant difference in COD level (p>0.1) between influent and effluent of the substrate non-added system due to that wastewater COD was unavailable for microbial growth and washout phenomenon occurred. COD reduction in substrate added system was improved by increasing hydraulic retention time (HRT). When HRT was operated at 16 hr, total COD in effluent was 151 mg/L, but the soluble COD reached to around 90 mg/L that could meet to the Effluent Standards (＜100 mg COD/L). The difference between total and soluble COD might be due to high SS (biomass) levels (32~109 mg/L) found in the effluent of substrate added system. Therefore, use of a sand filter or a subsurface flow constructed wetland following the biological process for polishing the biologically treated effluent is expected to satisfy both COD and SS (＜30 mg SS/L) effluent standards. It is also suggested that the domestic (nutrient containing) wastewater produced in factory area could be collected and mixed with the chemical treated wastewater to replace part of external organic nutrient and save some of material cost. |
