摘要
中密度纤维板生产废水的成分复杂,属难处理的工业废水。本文根据江苏某中纤板公司生产废水水质(COD_(Cr)为6000~30000mg/L;BOD_5/COD_(Cr) (B/C)为0.2~0.3),采用混凝-Fenton氧化法对其进行预处理以利于后续生化处理。
考虑到混凝效果和后续Fenton反应要求,确定聚合硫酸铁(PFS)作为处理该废水的无机混凝剂,并考察了主要工况条件对废水处理效果的影响,在此基础上研究PFS和有机助凝剂PAM联合投加时各项参数对处理效果的影响,得出混凝最佳工艺参数如下:PFS投加量为1.8g/L(原水COD_(Cr)为10110mg/L),快速搅拌(300r/min)30s,PAM投加量为10mg/L,慢速搅拌(60r/min)90s,沉淀120min。在最优混凝工艺条件下,废水经混凝处理后COD_(Cr)和SS去除率分别为60.8%、87%,出水pH为4.15,Fe~(2+)浓度为130.88mg/L,废水的zeta电位由处理前的-13.3mv上升到了-3.79mv,通过粒径分析,发现混凝处理对粒径为1—100μm的颗粒起到了较好的去除效果。
为了改善废水的可生化性和进一步降低废水的有机负荷,选择Fenton法对混凝出水进行进一步处理。实验得出Fenton氧化工艺的最佳参数如下:不调节混凝出水的初始pH、利用混凝出水中含有的Fe~(2+)(浓度为120~180 mg/L)、Fe~(2+)与H_2O_2的摩尔比为0.05,反应时间为40min后用NaOH调节废水的pH值至8~8.5,沉淀出水,Fenton氧化阶段的COD_(Cr)去除率达62.5%。
将混凝和Fenton氧化在最佳工况条件下联合使用, COD_(Cr)去除率达到了80.5%。此外,还考虑了将此工艺运用于工程实践中的可行性,在不影响后续生物处理的前提下将PFS的投加量改为0.75g/L,摩尔比改为0.3,在此条件下研究了混凝—Fenton氧化的连续流实验,COD_(Cr)去除率达到66%,每吨废水的预处理价格仅为3.1元。与此同时,通过GC-MS分析了处理前后的水质,发现混凝处理后水中大部分有机物得以去除,而一些环状有机物仍然残留,而经过Fenton氧化处理后部分环状有机物被转化为直链有机物。由此可见通过这种预处理改变了该废水的水质,使其更易于生物处理。
Medium density fibreboard (MDF) wastewater is one kind of refractory industry wastewater has complicated components.The combined coagulation-Fenton oxidation process was adopted for the pre-treatment of MDF wastewater which was originated from a wood company of Jiangsu (COD_(Cr) about 6000~30000mg/L;BOD_5/COD_(Cr) (B/C) ratio 0.2~0.3).
In consideration of the coagulation effect and the request of the Fenton oxidation process. Polyferric Sulfate(PFS) was choosen as the best inorganic coagulant compared to the others, so it was chosen as the coagulant for the MDF wastewater. The main condition were investigated, based on it, the research of combination of organic coagulant PAM and inorganic coagulant PFS has been studied, The optimal operation parameters of coagulation were determined as follows: the initial pH value, PFS dosage of 1.8g/L(the COD_(Cr) of MDF effluents is 10110mg/L), high speed agitation of 300 r/min with 30s, PAM dosage of 10mg/L,low speed agitation of 60r/min with 90s and precipitation time of 120min.After coagulation, 60.8% COD_(Cr) and 87% SS removal were achieved;The pH value was 4.15;The Fe~(2+) concentration of the water was 130.88mg/L;The zeta potential increased from -13.3mv to -3.7mv and the suspended particles of 1-100μm were nearly removed.
In order to further improve the biodegradability and reduce the organic load of MDF wastewater, Fenton oxidation process was selected for the sequencing treatment of the effluent. Optimum conditions of Fenton oxidation process for treating the effluent of coagulation were determined as: initial pH of the wastewater treated by coagulation,use the Fe~(2+) contained in the effluent which has been treated by coagulation(the concentration of Fe~(2+) is about 120~180mg/L), the nFe~(2+)/nH_2O_2 is 0.05,reacting for 40mins,pH was then adjusted to 8~8.5. 62.5% COD_(Cr) has been removed during the Fenton oxidation period.
The combination of coagulation and Fenton oxidation was taken into consideration,and the COD_(Cr) removal was 80.5%,it has achieved a good effection. The cost performance of this process has been considered, the PFS dosage has been changed into 0.75g/L, and change the nFe~(2+)/nH_2O_2 into 0.3, under this condition, the continuos running was evaluate, and the COD_(Cr) removal efficiency was 66%,the price of treat the effluent is 3.1 yuan per ton. A GC-MS research was taken,the result shows that after coagulation,many organics was removed,but some organics which has a annulate structure were reserved and parts of those annulations was turned into linear chain organics after Fenton oxidation.The experiment verified the combined coagulation-Fenton oxidation process was effective for pre-treatment of MDF wastewater.
引文
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