Study On The Toxicity And Key Toxicants Of Waste-paper Effluents And Sludge

Paper industry in China was facing many problems, such as shortage of wood rawmaterial, energy shortages, environment pollution and other issues. Waste paper recycling andreusing was as an effective approach to solve these problems. However, with the rapiddevelopment of waste paper industry, more and more attention to the pollution discharge fromits effluents and sludge were caused. According to the paper recycling status andcharacteristics, in this paper, several kinds of typical effluents and sludge were chosen as theobject of study, which were deink stock effluent, comprehensive effluent, board effluent,physical-chemical sludge, biochemical sludge and board sludge. And then the toxicity and keytoxcicants from the effluents and sludge were analyzed in details, which measured based onbright luminescent bacteria acute toxicity test technology, TIE （Toxicity IdentificationEvaluation）, QSAR （Quantitative structure-activity relationship）, GC-MS （GasChromatography–Mass Spectrometry） and AAS （Atomic Absorption Spectrometry） analyticalmethods. Meanwhile with the section of paper mill wastewater treatment processes, thetransfer of toxicity and key toxicants were systematically analyzed. The results were in detailsas follows.The value of EC₅₀for acute toxicity in deinked effluent, which was produced from thetechnological flow of25t/d, was1.41%, reached the level of highly toxic. As far as the totalorganic load was concerned, the value was927kgCOD_cr/t·pulp, and the total TEF was680.832TU·m³/t·pulp, as well as equivalently10.99g HgCl₂/t·pulp. The component analysisresults of deink stock effluent was shown that, the key toxicants were phenol, dibutyl phthalate,toluene and ortho-xylene; for the organic pollutants, the key toxicants were phenol, dibutylphthalate, toluene and ortho-xylene, toxic unit and total toxic unit26.37%; for inorganiccontaminants, heavy metals in the effluent were the key toxicants, the contents of Cu, Ni, Pb,Cr and Pd were respectively0.142,0.081,0.218,0.040and0.050mg/L.In the discharge of comprehensive effluent from the technological flow of60t/d, the valueof EC₅₀for acute toxicity was75.92%, reached Moderately toxic level. The value of total organic load was3796.2kgCOD_cr/t·pulp, and the total TEF was39.51TU·m³/t·pulp, as well asequivalently0.2041g HgCl₂/t·pulp. Meanwhile it was detected about the component analys ofcomprehensive effluent that, for the organic pollutants, not detected; for inorganiccontaminants, heavy metals in the effluent were the key toxicants, the contents of Cu, Ni, Pb,Cr and Pd were respectively0.080,0.122,0.160,0.018and0.053mg/L.The value of EC50for acute toxicity in board effluent was24.40%, which was producedfrom the technological flow of30t/d, belonged to the level of toxicity. The total organic loadwas2064.24kgCOD_cr/t·pulp, and the total TEF was124.99TU·m³/t·pulp, equivalently0.6352gHgCl₂/t·pulp. In the board effluent, the organic pollutants were not detected. But for inorganiccontaminants, heavy metals in the effluent were the key toxicants, and the contents of Cu, Ni,Pb, Cr and Pd were respectively0.080,0.122,0.160,0.018and0.053mg/L.In general, the order of the toxic pollution loads was, deinked effluent> board effluent>comprehensive effluent, wastewater. But as a result of the different emissions of three papermills, organic pollution loads were in another order, deinked effluent <board effluent <comprehensive effluent.For the determination of paper sludge toxicity, it was found that a good correlation wasbetween extraction solution from paper sludge using hydrochloric acid and luminous intensityof luminescent bacteria. The experimental conditions were as follows, hydrochloric acid as thesludge extraction agent,0.3mol/L HCl （pH value0.9）, extraction time2h, extraction solutiontemperature25℃. The experimental results show that the board sludge was the maximumtoxicity. The physical-chemical and biochemical sludge both belonged to Moderately toxiclevel, and the value of EC50were85.86%and89.64%respectively. But the value of EC50about board sludge was67.04%, reached the level of Toxicty.Combined with TIE and AAS analysis technology, three kinds of waste paperpapermaking sludge were studied. The heavy metal contents of Cu, Ni, Pb, Cr and Pd wererespectively,111.3,52,79.4,19.1,23.0mg/kg in physical-chemical sludge;90.6,42.4,92.6,15.8,21.2mg/kg in biochemical sludge;55.2,52.2,107.4,19.2,24.6mg/kg in board sludg.From this analysis, in the paper mill sludge, key toxicants were Cu, Ni, Pb, Cr, Pd and otherheavy metals.Based on the toxicity and toxicity levels of waste paper effluents and sludge, combined with the section of paper mill wastewater treatment processes, the transfer of toxicity and keytoxicants were systematically analyzed in order to track key toxicants. Finally it was indicatedthat, for paper mill B, pollutant toxicity from comprehensive effluent B eventually wastransferred to the physical-chemical sludge and biochemical sludge, and the degradation oforganic toxicants and the transfer of inorganic heavy metals to the sludge were happened at thesame time. Compared with paper mill B, it was relatively simple about tracking toxicants frompaper mill C. The toxicity of board effluent （comprehensive effluent C） was transferred to theboard sludge. Actually it was the result that heavy metals in board effluent were transferred tothe sludge.Summarily, in this paper, it was systematically analyzed on the toxicity and the keytoxicants from waster paper effluents and sludge. Meanwhile it was based on the section ofpaper mill wastewater treatment processes for the purpose of tracking key toxicants. In total,for the future practical production, it was provided realistic basis on how to properly dischargeand treatment of effluents and sludge to avoid secondary pollution.