Pretreatment of Herbicides Production Wastewater by Different Electrolyte Fillers

Jingliang XlE，Hao DU，Zhong PENG，Fuhao WANG

1.School of Environmental and Municipal Engineering，Qingdao University of Technology，China；

2.UDIC of Qingdao Energy and Environment Ltd.Qingdao 266000，China

Pretreatment of Herbicides Production Wastewater by Different Electrolyte Fillers

Jingliang XlE1*，Hao DU1，Zhong PENG2，Fuhao WANG2

1.School of Environmental and Municipal Engineering，Qingdao University of Technology，China；

2.UDIC of Qingdao Energy and Environment Ltd.Qingdao 266000，China

［Objective］The aim was to study the pretreatment effect of herbicides production wastewater by different types of micro-electrolysis filler.［Method］The research performed comparison on the effects of three types of micro-electrolysis filler treatment of pesticide wastewater by changing the role of time and pH.［Result］The results showed that the best treatment effect was spherical packing，followed by tooth filler；poor treatment effect and easy to harden were iron shavings.With pH of the influent of 2 and reaction time of 160 min，the removals of CODcr and chromaticity which was with spherical packing reached 24.79%and 97.5%；the removals of CODcr and chromaticity which Dentate micro-electrolysis filler treated reached 21.74%and 93.75%.With pH of the influent at 3 and reaction time of 120min，the removal of CODcr and chromaticity which was treated with iron ingot reached 13.59%and 87.5%.［Conclusion］By comparison analysis，the spherical packing is better suited to handle wastewater.

Spherical micro-electrolysis filler；Dentate micro-electrolysis filler；Cast iron ingot；Pesticide wastewater；CODcr；Chromaticity

T here are many advantages of herbicides in weed control such as labor-saving，efficient and thorough，and they are playing an increasingly important role in agricultural production.Nevertheless，the wastewater generated during the production of herbicides is characterized by high concentrations，complex composition，high toxicity and mineral contents，and to be difficult treated，thus the pretreatment of this kind of wastewater is particularly important［1-4］.At present，the common treatments are mainly coagulation，adsorption，extraction，electrochemistryand oxidation，and so on. Coagulation is chiefly used to remove fine suspended matter and colloidal pollutants［5］in wastewater.Technologies like electrochemistry，photocatalytic on are merely applied in China for t1oxidation and wet air oxidation have good effects but require higher cost［6］.

Micro-electrolysis is a result of comprehensive effects involved in roles such as flocculation，adsorption， bridge，swept volume，co-precipitation，electro deposition and electrochemistry，through which pollutants can be removed effectively and biodegradability［7-8］of wastewater can be improved.Micro-electrolysis has been widely used and achieved better effects［9-15］in treating petrochemicalwastewater，dye wastewater，pharmaceutical wastewater and other respects.There are also reports on the research of treating pesticide wastewater by micro-electrolysis.Wenbin YONG et al.［16］investigated the treatment of pesticide wastewater such as triazophos，bisultap，and monosultap etc.With electrolyte in which the ratio of iron to carbon is 2 to 1，the removal of CODcr，chroma，arsenic and phosphorus reached to more than 60%after treatment；Jingliang XIE et al.［17］utilized spherical packing to process original mixed wastewater of fomesafen and trifluralin，under the optimal reaction conditions，the removal of COD can reach to 26.3%，chromaticity and TP over 85%，and BOD5/COD varies from 0.10 to 0.35.

Different shapes of iron-carbon fillers，produced by the integration of multiple alloy and catalyst and the utilization of high temperature microporous activated technology，together with traditional cast iron ingots，were preferred for the treatment of mixed wastewater of fomesafen and trifluralin.The effects of dealing time and pH of different kinds of fillers on the treatment were investigated，for the reference of suitable choice of microelectrolysis filler for the treatment of that kind of pesticide wastewater and practical application.

Materials and Methods

Test sample

Wastewater was taken from a regulating pond of sewage station of apesticide plant in Qingdao，Shandong，and the company’s primary varieties of pesticide are fomesafen and trifluralin.The sample was reddishbrown in appearance and pungent in smell，its amount of CODcr was 3 275 mg/L，with pH 1.84 and amount of TP 228 mg/L，totally inorganic phosphorus and chroma 2 400 times.

Test program

By comparing rermoval effects between the three types of microelectrolysis fillers on the CODcr and chroma of pesticide wastewater in different reaction time and at different pH，we can find the optimal control parameters.

Results and Discussion

Effect of time on the treatment of different micro-electrolysis fillers

Add the water of regulating pond to the three beakers which contain a litre of spherical micro-electrolysisfiller，dentate micro-electrolysis fillerand cast iron ingot respectively until it was on a level with the filler.Observe treatment effects of different micro-electrolysis fillers in different reaction time，as shown in Fig.1-Fig.2.

From Fig.1 it can be concluded that:the CODcr of pesticide wastewater gradually decreased with the lapse of reaction time，when the reaction time reached to 80 min，the cast iron ingot achieved the optimal removal effect of CODcr，which dropped from the initial 3 275 mg/L to 2 830 mg/Land the efficiency was 13.6%，afterward，CODcr had a slight rise as time went on.While as to spherical filler and dentate filler，their removal effect of CODcr reached the best at thetime of 160 min，at that time，after the treatment of spherical filler anddentate filler respectively，the CODcr in pesticide wastewater respectively dropped to 2 463 and 2 563 mg/L，and the efficiencies were 24.8% and 21.7%.

Efficiency at different retention times

Fig.2 showed that，with the lapse of treatment time，the chroma of the watersample decreased afterthe treatment of three fillers.At 120min，the chroma of wastewater reached the lowestafterthe castiron ingot’s treatment，which was 270 times and the removal rate was 88.7%.As time went on，the color of the wastewater began to reverse；within the same time，for spherical filler，the chroma dropped to 90 times and the removal rate was 96.2% which increased merely 1.2%with time going on，while for tooth filler，the chroma was 240 times and the removal rate was 90%，when time increased to 160 min，the removal was 93.7%.efficiency at different retention times

From Fig.1 and Fig.2 we can concluded that the removal of CODcr and chroma increased with time and tended to be steady at last.It was because that with the growth of reaction time，the mount of newly generated Fe2+and［H］was increasing，thus making oxidation and reduction much more thoroughly，and chromogenic organic compoundsin wastewater could be more removed in mount or destroyed in structure，and even mineralized which was the aim.However，as time went on，the pH would raise，the efficiency of the micro-electrolysis would decrease and the organic compounds which can be processed by microelectrolysis would run out，in consequence，the removal of CODcr and chroma would become stable in the later stage reaction.Therefore，it was clear that the optimal treatment time for spherical filler and dentate filler was 160min and cast iron ingot 120min.

Effect of pH on the treatment of different micro-electrolysis fillers

Given that the filler was one litre and the treatment time was optimal（spherical and dentate fillers 160min and cast iron ingot 120min），we investigated the effect of pH on the treatment of pesticide wastewater with different fillers.

From Fig.3 and Fig.4 we can see that pH had significant impact on the removal of CODcr and chroma at the optimal treatment time.The lower pH was，and the lower the CODcr was，the higher the removal efficiency was，and the effluent color was lower at the same time.It was because that when the pH value was in low level，the efficiency of micro-electrolysis was relatively high，Fe2+，a fine flocculant generated a large mount in this process，could adjust the pH to basic，and when there was O2in the solution，they can formulate flocculating settling Fe（OH）2and Fe（OH）3.Flocculating settling can adsorb the original suspension in the wastewater and insoluble matter produced by micro-electrolysis as well as remove chromogenic insoluble organics which can decrease chrominance. When pH was 2，the optimal removal of CODcr for spherical and dentate fillers were respectively 24.8%and 2.17%，while the it was 1.36%for the cast iron ingot when pH reached 3. With the increase of pH value，the removal gradually decreased.When pH was 6，the removal of CODcr which spherical filler，dentate filler and cast iron ingot treated were 9.1%，9.9% and 9.5%；When pH was 2，the three fillers reached the optimum removal which were respectively 97.5%，93.7% and 88.7%.When pH was 6，their removal of chroma decreased to 75%，75%and 81.2%.By combining the removal effectsof CODcr and chroma it can be concluded that spherical filler and dentate filler had the optimal treatment effect when the time was 160min and pH was 2，and the optimal condition for cast iron ingot was 120 min and pH 3.

Conclusion

（1）According to the research on the wastewater in regulating pond，the results showed that:The best treatment effect is spherical packing，followed by tooth filler；poor treatment effect and easy to harden are iron shavings.

（2）The treatment effect became better gradually with time，the optimal treatment time for spherical filler was 160 min when CODcr dropped to 2 463 mg/L and chroma was 60 times，at the same time，the CODcr and chroma of dentate filler dropped to 2 563 mg/L and was 150 times；when the time was 120 min，cast iron ingot reached the best removal effect of CODcr and chroma and they are respectively 2 850 mg/L and 270 times.

（3）The lower the pH was，the better the removal effect of CODcr and chroma in water sample was.Spherical filler and dentate filler had the optimal treatment effect when time was 160 min and pH was 2，the removal of CODcr were 24.8%and 21.7%and of chroma were 97.5%and 93.7%respectively，while for cast iron ingot the optimal condition was 120 min and pH 3，and the removal of CODcr and chroma were 13.6%and 87.5%.

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Responsible editor：Xiaoxue WANG

Responsible proofreader：Xiaoyan WU

*Corresponding author.E-mail:jingliangx@163.com

Received:October 5，2015 Accepted:November 16，2015