The Formation Of Solid Phase Substances In Coking Wastewater Treatment And Its Disposal Life Cycle 3E Assessment

Coking wastewater is generated in the production process of coal chemical industry.Due to the complex constituents,wastewater treatment is composed of chemical,biological or physicochemical technologies.In the treatment process,most contaminants can be removed.However,a variety of solid-phase substances,including tar,sludge and crystal salt were produced during the treatment of coking wastewater.Even if these substances may be pollutants,they have the potential for being resources.At present,there is a lack of energy,economic and environmental assessments about solid-phase substances disposal technologies.In this study,desalination was added to"pretreatment+biological treatment+advanced treatment",which is a practical treatment process of coking wastewater.The formation mechanism of of tar,physicochemical sludge,biological sludge and crystallization of mixed salt was proposed,the output calculation and treatment method evaluation model were established.Besides,the sources of solid-phase substances were investigated.Based on this,the calculation model of the solid-phase substances was established,which can provide data support for decision-making of solid-phase substances treatment scheme.The choice of solid-phase substance disposal technology is a tough multi criteria decision-making problem,which is required to balance the energy consumption,environmental impact and economic cost.Combining the multi-attribute utility theory with life cycle assessment method,the energy,environment and economic indicators were quantified to evaluate the different disposal methods of three kinds of solid substances.In the assessments,the weight of factors was allocated by AHP.Based on the life cycle 3E（Energy,Environment and Economy）assessment,the overall decision-making model of solid-phase substances disposal is established,which can provide a reference for the disposal of solid substances.Taking the second stage project of coking wastewater treatment in the coking plant of Baowu Group Guangdong Shaoguan Iron&Steel Co.,Ltd.as the research object,the production of actual solid-phase substances was calculated by using the operation parameters and water quality statistical data of the A/O/H/O（Anaerobic/Aerobic/Hydrolysis/Aerobic）fluidized bed process.The output of tar,physicochemical sludge,biological sludge（moisture content is 80%）and crystallization of mixed salt was 0.268 t·d^-1、8.35 t·d^-1、6.10 t·d^-1 and 2.84t·d^-1,respectively.For per cubic meter of wastewater,the yields of tar,physicochemical sludge,biological sludge（moisture content is 80%）and crystallization of mixed salt were 0.186 kg·m^-3,5.80 kg·m^-3,4.24 kg·m^-3 and 1.97 kg·m^-3,respectively,which were verified with the annual statistical data of actual production.The various disposal methods of tar,sludge and industrial salt were arranged and divided into eight disposal schemes.Taking the annual output of three kinds of solid-phase substances as the functional unit,from the perspective of energy consumption,environmental impact and economic benefits,the disposal scheme of solid-phase substances was analyzed,and the weight to energy,environment and economy was given by AHP in this work,which were 16.3%,29.7%and 54.0%respectively.The life cycle assessment results showed that deep processing of tar to produce high-value products,sludge pyrolysis to produce combustible gas,solid product adsorbents,bio oil and crystal salt purification were the best scheme for the disposal of solid-phase substances produced in the process of coking wastewater treatment.The balance among the minimum energy consumption,the minimum environmental impact and the maximum economic benefit was achieved,and the property transformation of solid-phase substances between hazardous wastes and products/resources was realized.The analysis of variability proved the robustness of decision results.It is necessary to combine advanced technologies as well as strict laws and regulations to manage the quality and fate of solid-phase substances produced in the process of coking wastewater treatment,which can realize the coordination of energy recovery,environmental friendliness and economic benefits.