Toxicity Identification And Promising Treatment Methods For Typical Non-Biodegradable Wastewater

With the improvement of people’s living standard and development of modernindustry, the variety and quantity of the pollutants discharged into the environment iscontinuously increasing. Among them, the non-degradable wastewater attracted moreand more attention. The non-degradable wastewater is characterized by biologicalaccumulation and high toxicity to ecosystem; it may cause severe damage toecosystem and environment without appropriate treatment.This research mainly studied the treatment methods of three typicalnon-degradable wastewater: chemical industrial wastewater, old landfill leachate andthe secondary effluent with pharmaceutical and personal care products （PPCPs）frequently detected, which attracted widely attention. And this research can beclassified to3parts:1. Took old chemical industrial wastewater for example, emploied wheat rootelongation inhibition toxicity experiment for the first time and conventional daphniamagna toxicity experiment and identified the major toxic pollutants were Cl-andheavy metal Cu²⁺, Pb²⁺and Zn²⁺.Based on the high salinity characterization of the wastewater, co-treatment ofmunicipal wastewater and chemical industrial wastewater by the demand aerationtank-intermittent aeration tank （DAT-IAT） process used in TEDA wastewatertreatment plant was evaluated, and the chemical oxygen demand （COD）, totalphosphorus （TP） and total nitrogen （TN） removal efficiency of the mixed wastetwatercan reach up to85.08%,89.29%and96.54%, the toxicity unit of the wastewater aftertreatment was0.5TU. This result demonstrated that co-treatment of municipalwastewater and chemical industrial wastewater is a feasible and cost effectivemethod.2. Based on the conventional pollutants removal and toxicity reduction, thetreatment efficiency of old landfill leachate by the combined process of coagulationand powder active carbon adsorption was evaluated. Polyferric sulfate （PFS）(dosage 0.3g Fe³⁺/L) showed the best treatment efficiency, with the removal of COD, turbidity,solid suspension （SS） and toxicity up to70%,99%,93%and74%at pH5.5. UsingPFS coagulated wastewater as the influent of adsorption and after powder activatedcarbon （PAC） adsorption （10g/L） treatment for90min, the residual COD was about407mg/L. The total COD and toxicity removal efficiency of this combined processwas86%and78%, respectively.3. Optimized the degradation efficiency and studied the degradation kinetics ofPPCPs frequently detected in secondary wastewater, including acetaminophen,atenolol, diclofenac, metoprolol, dilantin, pentoxifylline, caffeine, iopromide,fluoxetine, trimethoprim, propranolol, sulfamethoxazole, ibuprofen, naproxen,gemfibrozil, DEET, carbamazepine, oxybenzone, bisphenol-A, atrazine, by Fentonand Fenton-like process; Transformation and oxidation byproducts of effluent organicmatter （EfOM） in Fenton and Fenton-like process was also quantified, and thefeasibility of absorbance and fluorescence surrogates used to predict PPCPsdegradation and EfOM oxidation was also explored, the conclusions are as following:（1） Considering the degradation efficiency of PPCPs and treatment cost, theoptimal conditions for Fenton process were: molar ratio of H₂O₂/Fe²⁺of2.5, Fe²⁺dosage of10mg/L, pH3, reaction time of30min; the optimal conditions forFenton-like process were: molar ratio of H₂O₂/Fe³⁺of2.5, Fe³⁺dosage of10mg/L,pH3, reaction time of120min. Under these conditions and the initial dissolvedorganic matter （DOC） of8.287mg/L, the removal efficiency of PPCPs can reach upto90%.（2） The degradation of PPCPs by Fenton process follows combined first orderreaction kinetic; the degradation of diclofenac, fluoxetine and gemfibrozil byFenton-like process follows second order reaction kinetic, and the degradation ofother PPCPs by Fenton-like process follows first order reaction.（3） The reaction constants of PPCPs and OH （kPPCPs-OH） calculated based on thecompetition kinetic model were close with the previously reported values, except thatthe values for DEET, trimethoprim, ibuprofen, diclofenac, caffeine and gemfibrozilwere a little different from reported values because of the different reaction condition.This confirmed that PPCPs was removed by OH oxidation during Fenton and Fenton-like reaction other than coagulation effect.（4） Fenton and Fenton-like reaction caused30%and38%of DOC removal byOH oxidation and coagulation. Size exclusion chromatography （SEC） datademonstrated that Fenton and Fenton-like process preferentially remove highmolecular weight EfOM molecules and break them down into smaller fragments.（5） The oxidation byproduct of EfOM by Fenton and Fenton-like process wereformate, acetate, oxalate and less prominently, formaldehyde, acetaldehyde,propionaldehyde and glycolaldehyde. The yields of carboxylic acids and aldehydes ascarbon were11.62%and1.01%of the initial DOC by Fenton process under thereaction condition of molar ratio of H₂O₂/Fe²⁺of2.5, Fe²⁺dosage of20mg/L, pH3,reaction time of30min; The yields of carboxylic acids and aldehydes as carbon were13.2%and1.34%of the initial DOC by Fenton-like process under the reactioncondition of molar ratio of H₂O₂/Fe³⁺of2.5, Fe³⁺dosage of20mg/L, pH3, reactiontime of120min.（6） The UV absorbance of EfOM decreases with the increase of theFenton/Fenton-like reagent dosage and reaction time. The differential absorbancespectra show a prominent feature at wavelength265-275nm. This feature, and thedecrease of UV254, SUVA254value may demonstrate the preferential removal ofaromatic organic matter.The UV absorbance spectra were sensitive to the inorganic matter. Aftereliminating the interference, the relative changes of absorbance at254nm (donated asA₂₅₄/A₂₅₄⁰) were strongly correlated with PPCPs removal, OH exposure and theconcentration of carboxylic acids irrespective of whether the wastewater was treatedwith Fenton process or Fenton-like process at any Fe doses and treatment times. Thisdemonstrated that A₂₅₄/A₂₅₄⁰could be used as a surrogate to predict the PPCPsdegradation and EfOM oxidation extent in advanced oxidation processes.（7） According to the three dimension fluorescence spectra, EfOM can beclassified as protein-like species/soluble microbial products, humic-like species andfulvic-like species. Protein-like species/soluble microbial products are the mostreadily removed part by Fenton and Fenton-like processes.The total integrated fluorescence relative change （TFhumic/TFhumic0） and peak intensity relative change （PFhumic/PFhumic0） of humic-like species were stronglycorrelated with PPCPs degradation, OH exposure and carboxylic acid concentrationirrespective of whether the wastewater was treated with Fenton process or Fenton-likeprocess at any Fe doses and treatment times. This demonstrated that TFhumic/TFhumic0and PFhumic/PFhumic0could be used as surrogates to predict the PPCPs degradationand EfOM oxidation extent in advanced oxidation process.