摘要
伴随着核技术的发展,放射性废水的直接排放会造成局部水域的放射性核素污染。研究去除核污染产生的放射性元素对于促进清洁能源生产、保障人体健康、保护环境具有积极意义。膜分离技术作为一门新型学科,结合化学沉淀技术处理放射性废水,具有工艺简单、自动化程度高、占地少等优点。本文主要研究化学沉淀-微滤工艺处理含锶废水的可行性和优化方案。
整个试验分为初步试验和小试试验两个部分。初步试验主要探索了处理含锶废水需要的沉淀剂,最终选择了Na2CO3作为沉淀剂,同时也研究了减缓膜污染的技术措施,确定在沉淀器和膜反应器中分别投加FeCl3。小试试验共进行三个阶段,第一、二阶段均采用间歇运行的方式,Na2CO3的投加量分别为2000 mg/L和1000 mg/L,结果显示:一、二阶段工艺的平均去污因数(Decontamination Factor, DF)分别为220、154,浓缩倍数(Concentration Factor, CF)分别为302、462,尽管第一阶段平均DF较低,但处理水量和膜污染程度均优于前者。另外针对间歇运行中反应器启动的前3个小时出现的出水锶浓度较高的现象,第三阶段进行了连续运行的试验研究,除反应器运行方式改变外,其它工艺参数均和二阶段相同,结果显示:平均DF和CF分别为145、480,连续运行方式可以消除间歇运行产生的锶返溶问题。
采用化学沉淀-微滤工艺含锶废水时,镁的去除率较低;铁、钙基本被全部去除;相关阴离子基本没有去除。除出水pH值稍高外,出水可以很好的满足《污水综合排放标准》(GB8978-1996)。
针对工艺运行管理过程中的膜污染问题采取的低压操作、间歇运行、控制曝气强度和周期性的排泥洗膜等技术措施,可以降低膜比通量下降的速率。
试验结果显示化学沉淀-微滤工艺可以有效处理含锶废水,该工艺具有流程简单、自动化程度高、能耗低、污泥产生量少、出水水质优良等诸多优点,是低放废水处理的理想选择之一。
Along with the development of nuclear technology, the direct discharge of radioactive wastewater can cause the radionuclide contamination of local waters. Study on removal of radioactive elements produced by nuclear contamination has a positive significance in promoting clean energy production, protection of human health and environment. Compared to traditional process, the membrane process, emerged as a new technology, has many advantages such as simple process, higher degree of automation, less area required, when combined with chemical precipitation technology and separation technology to treat radioactive wastewater. The feasibility and optimization program of treating wastewater containing strontium by chemical precipitation-microfiltration was focused in this paper.
The whole experiment was composed of preliminary experiment and pilot-scale experiments. In the preliminary experiment, chemical precipitation agent to deal with wastewater containing strontium is mainly studied, and Na2CO3 was chosen in the end. In addition, technical measures to mitigate membrane fouling was also discussed, and finally, FeCl3 was decided to be dosed into the sedimentation tank and membrane reactor. Pilot-scale experiments can be divided into three stages. In the first and second stage, the mode of intermittent operation was used, and the dosage of Na2CO3 was 2000 mg/L and 1000 mg/L, respectively. The results showed that the average decontamination factor (DF) of the first and second stage were 220, 462, and concentration factor (CF) were 302, 462. Although the average DF of the second stage was lower than the first one, the volume of treated wastewater and the degree of membrane fouling were improved, compared with the former. In addition, to cope with the problem that the strontium in the effluent was much higher during the first three hours after the reactor was started up, the experiment of continuous operation was carried out in the third stage, in which all parameters were same with the second stage, except for the mode of process operation. The results showed that the average DF and CF were 145, 480. The mode of continuous operation could eliminate the problem, that strontium had re-solved to the reactor in the mode of intermittent operation.
While integrated chemical precipitation-microfiltration process was used to treat wastewater containing strontium, the removal rate of magnesium was much lower, ferrum and calcium were removed completely, and the related anions were not removed. In addition to higher pH value, the effluent could meet the requirement of the Integrated Wastewater Discharge Standard (GB8978-1996).
During the operation of the experiment, many technical measures, including low-pressure operation, intermittent operation, control of aeration intensity and periodic sludge discharge, were adopted to mitigate membrane fouling, and could be testified to reduce the rate of decreasing membrane specific flux.
The results showed that integrated chemical precipitation-microfiltration technology could effectively deal with wastewater containing strontium. The process for the treatment of the wastewater containing strontium has many advantages, such as simple process, higher degree of automation. To sum up, the integrated chemical precipitation-microfiltration process is one of ideal choices to treat lower radioactive wastewater.
引文
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