An Approach To Determining Regional Emission Control Objectives Of Heavy Metals In Wastewater

Heavy metal pollution in water has done harm to regional environment, andbrought threat to human health and ecological security. Since the lack ofappropriate technical means to support, the current formulating method ofregional emission control objectives of heavy metals in wastewater is limited totarget total content control in China, which ignored the restriction of waterquality and sediment quality. So this study contributes three formulatingmethods of regional emission control objectives of heavy metals in wastewaterbased on different control concepts. To solve technical problems with totalcapacity management of heavy metals, this study contributes a model of heavymetal transport-transformation in river as a tool for quantitative calculation.The first formulating method transplanted directly the requirement of “the12thFive-Year Plan for comprehensive prevention and control of heavy metalspollution”，shorted as National Plan in the following，to local based on Top-downcontrol concept. The second formulating method combined the requirement of NationalPlan with the the requirement of local water quality. This method taked the relationshipbetween total emission and water environmental quality into account to some extent.The third method considered the specificity for heavy metals which were in the firstclass of pollutants of “Integrated Wastewater Discharge Standard”. Since the thirdmethod applied total capacity management to heavy metal control based onone-dimensional model of phase separation in river, it combined three constraintconditions, which were the requirement of outfall standards, the demand of waterenvironmental capacity and sediment capacity.Take Prefecture of Honghe in Yunnan Province as a case, which existed seriouslead pollution, some arsenic pollution and slight cadmium pollution. Lead, arsenic andcadmium were prioritized as control targets by considering the characteristics oftotal emission, emission contribution to the state, coordination betweenemission contribution and economic contribution, pressure of emissionreduction and requirements of water environmental improvement. Thecalculations of three formulating methods were developed with lead, arsenic andcadmium. The results of the first method showed that total emissions of lead, arsenic and cadmium in2020should reduce by20%,86%and95%compared with that in2010,which was too difficult to achieve for such a region with low environmental efficiencylevel. While the control objectives of arsenic and cadmium, which were difficult toimplement, may become a mere formality, and the significance of a substantialreduction for water quality improvement was not clear. The reduction rates of thesecond method were30%、45%and15%. To guarantee the achievement of bothemission reduction and economic development, the discharge intensities ofheavy metals were need to be reduced to quite low. The second method wasfeasible to be applied in estimating the total emissions for the improvement ofwater quality without mathematical modeling conditions, simple and practical.The reduction rates of the third method were72%，37%，32%, based on thecontrol objectives calculated by one-dimensional model of phase separation inriver. Sediment quality was more constrained in formulating regional emissioncontrol objectives of heavy metals compared with water environmental quality.Since the third method combined the requirement of outfall standards, the demand ofwater environmental capacity and sediment capacity, the calculated objective valuesmay serve to total capacity management.