Treatment Of Swine Wastewater Using Bioflocculation And Adsorption With Chemically Modified Zeolite

Over the past decades, with the rapid development of the scale and intensifypoultry farming in our country, the environmental pollution is becoming much moreserious. Nitrogen pollution in livestock wastewater is the most prominent. At homeand abroad, the anaerobic-aerobic method was mainly used in the treatment of swinewastewater, although the most of the organic pollutants in wastewater were degradedin the anaerobic tank, the concentrations of nitrogen were still high in the digestedswine wastewater. Biological systems （biological nitrification–denitrification） haveprovided an effective solution, where ammonium was firstly transformed to nitrite,then to nitrate, and finally to nitrogen gas. However, since biological systems do notrespond well to high shock loads of ammonium, unacceptable peaks over thedischarging levels may frequently appear in the effluent ammonium concentrations.Besides this, the treatment of ammonium nitrogen wastewater of low organic contentby a biological process usually needs to be supplemented with extra carbon source,which may add to the treatment costs. In such solution, the efficient removal oforganic pollutants using bioflocculant has been considered as a potential solution tothe toxicity and the environmental pollution in recent years, and the ammoniumadsorption using zeolites as adsorbent are gaining on interests.Based on the degradation of the high concentration of organic pollutants bybioflocculants and adsorption of high-level of ammonium by MgO-modified zeolite,this paper presents a study of the treatment of digested swine wastewater using thecompound of bioflocculant and MgO-modified zeolite. The response surfacemethodology （RSM） was selected to establish the two quadratic models of COD andammonium removal efficiencies to remove the organic pollutants and recycle the highconcentration of ammonium. On the one hand, the production and performance of thebioflocculant MBFR3from swine wastewater and activated sludge were investigatedin the degradation of the high concentration of organic pollutants. On the other hand,the performance and kinetics characteristics of a zeolite modified by calcined withMgO were examined in the adsorption of high-level of ammonium. On this basis, theremoval of organic pollutants and ammonium was cemented by adding MBFR3in thecoagulation of digested swine wastewater by MgO-modified zeolite, and hence, COD,ammonium and turbidity could be maximized remove from the wastewater. A high flocculant–producing bacteria R3, screened from activated sludge, wasidentified as Rhodococcus Ruder by a series of physiological and biochemicalexperiments and16S rDNA. This paper presents a study of production andperformance of a bioflocculant from bacteria R3, results showed that the optimalcomponent of1.0L fermentation medium for bioflocculant production was distilledwater1.0L,20g sucrose,4.0g urea,1.0g yeast extract,10.0g NaCl,2.0g MgSO₄,5.0g K₂HPO₄, and2.0g KH₂PO₄. The swine wastewater and activated sludgepre–treated by alkaline–thermal （ALT） treatments can be used as substituting mediumfor bioflocculant production, without adding any other organic and nitrogencompounds. The models about the strain growth, bioflocculant production, andconsumption of sucrose were described, through the comparison of experimental dataand the corresponding calculated values from the models, it was found that the datajoint well. Analysis of the purified bioflocculant by chemical methods indicated thatthe main component was a protein （99.7%）, with an approximate molecular weight of3.99×10⁵Da. Flocculating rates of kaolin clay （4.0g/L） was above90%when thebioflocculant （MBFR3） dosage was adjusted in the range of10-30mg/L, andincreased with the increasing dosage, and a maximum flocculating rate of96.8%wasachieved when the pH was adjusted to8.0. This bioflocculant also processed anindustrial potential for treatment of digested swine wastewater, when the pH valuewas adjusted to7.0-9.0and20mg of MBFR3was added into1.0L of the sample, themaximum removal efficiencies of COD, ammonium and turbidity of47.2%,41.9%,and72.9%were achieved. In addition, the flocculation mechanism reflected that theflocculation was completed by charge neutralization and bridging mechanism byaddition Ca²⁺in two steps, coagulation and flocculation. First step was thecoagulation, in which Ca²⁺draw closer to the negatively charged particles throughcolumbic attraction and Ca²⁺–particle complexes were formed. Ca²⁺reduced thethickness of the diffuse double layer of adjacent particles and hence, reducing theinter-particle distance between particles. Second step was the flocculation, in whichbioflocculants act like a bridging agent of two or more Ca²⁺–particle complexes andreduces inter-particle distances through the ionic bond mechanism, and bridgingoccurred after the Ca²⁺–particle complexes adsorbed onto the bioflocculants chains.Restated, particles adsorbed to a bioflocculant molecular chain, and they could adsorbsimultaneously to other chains, leading to the formation of three-dimensional flocs,which were capable of rapid settling.It can be concluded that the zeolite modified by calcined with MgO at400oC has a good performance for ammonium removal with adsorption capacity as high as24.7mg/g, an increase by96.1%compared to the zeolite not calcinated （12.6mg/g）. Arapid increase trend was observed when the zeolite dosage ranging between5and30g/L, and58.6%of ammonium removal efficiency was achieved at zeolite dosage of30g/L. There is an optimum pH range for ammonium adsorption, as solution pH rangingfrom7.0to9.0, the highest ammonium removal efficiency of58.9%was achieved atpH being8.0, and it is likely that ammonium was converted into “free” ammonia（NH3） at pH values above9.0, which can not be exchanged. It is clearly that theammonium removal from digested swine wastewater occurred rapidly within the first30min, and the sorption equilibrium began to establish itself within80min. Theadsorption kinetics indicated that the intraparticle diffusion was the rate-limiting stepfor ammonium adsorption. The adsorption isotherm results indicated that the theoryammonium adsorption capacity of MgO-modified zeolite decreased from29.1mg/g to27.4mg/g with the increasing experimental temperature from25to45oC. Comparedto Freundlich and Tempkin equilibrium, Langmuir model provided the best fit for theequilibrium data. Thermodynamic parameters were also determined in this study, thenegative value of Gibbs free energy change or adsorption energy （ΔG^θ） indicates thespontaneous nature of the adsorption process, the adsorption process was found to beexothermic as confirmed by the negative values of ΔHθ, and the negative value of ΔS^θshowed the decreased randomness at the solid–liquid interface during the adsorptionof ammonium by the modified zeolite. The main mechanisms involved in theadsorption are both ion exchange with mainly Mg²⁺and Ca²⁺and surface orintraparticle sharing between ammonium ions and functional groups, such as alkyl,carboxyl and hydroxyl groups.The central composite design, which is the standard RSM, was selected toinvestigate the interactions of parameters including the dosage of the MBFR3（x1）,modified zeolite （x2）, pH （x₃）,CaCl₂（x4） and contact time （x5）, respectively. The twoquadratic models for the five factors were established with COD and ammoniumremoval rate as the target responses. The optimal flocculent condition obtained fromthe two desirable responses, COD removal rate as100%and ammonium removal rateas100%, which deduced from the frequency of responses, were MBFR3of24mg/L,modified zeolite of12g/L, CaCl₂of0.16g/L, pH of8.3and contact time of55min.Under this optimal condition, COD, ammonium and turbidity removal rates wereappeared as87.9%,86.9%and94.8%, respectively.This dissertation fully focused on the flocculation mechanism of organic matters by bioflocculant MBFR3, the adsorption mechanism of ammonium by MgO-modifiedzeolite, and the performance of the compound of MBFR3and MgO-modified zeolitein the treatment of digested swine wastewater. The research results would provide afeasible way to solve the difficulties to achieve good removal efficiencies ofpollutants in the aerobic post-treatment over the world. The process conditions of thedigested swine wastewater treatment by the compound of MBFR3and MgO-modifiedzeolite were optimized by the RSM, and the two quadratic models of COD andammonium removal efficiencies established provide scientific foundation on theactual projects. The use of the compound was not only improving the pollutantremoval and recycling the ammonium nitrogen, but also avoiding the secondarypollution brought by adding PAC and PAM in wastewater treatment.