This paper reports a bioaugmentation process which is applicable to intensify the removal of co-contaminated pollutants in electroplating wastewater. Microbial consortia which constructed with organic degradation and heavy metals resistant strains could promote COD and Cu²⁺ removal efficiencies in a laboratory-scale hydrolytic-anoxic-oxic membrane bioreactor. In surface processing industrial parks, co-contaminated pollutants of low concentration of heavy metals and refractory organics, which were generally more difficult to remove than individual, will put an adverse impact on the biological treatment system in the long term operation. Although many screened strains and acclimated microbial consortia had shown strong heavy metal biosorption capacity in various wastewater [1, 2]. Few researches focused on the strains which had both strong organic degradation capacity and heavy metals resistance to the bioaugmentation of co-contaminated water.

In this study, five isolates were screened and identified as Burkholderia sp., Enterobacteria sp., Meyerozyma guilliermondii, Meyerozyma guilliermondii and Enterobacteria sp. Marking them as L1-L5. Evaluating their Cu²⁺ biosorption performance and organic degradation capacity under diverse pH values, temperatures, growth phases and Cu²⁺ concentrations. The bioaugmentation process was divided into four periods: period 1 (75 days, 3 mg/L CuO NPs), period 2 (75 days, 10 mg/L CuO NPs), period 3 (60 days, 10 mg/L CuO NPs + one-time bioaugmentation) and period 4 (60 days, 10 mg/L CuO NPs + repeated batch bioaugmentation). Using T-RFLP technology, the survival and persistence of the added strains in the reactor were further analyzed.

Results in LB broth of the isolates presented higher minimum inhibitory concentration (MIC) to Cu²⁺ than other reported microorganisms [3]. The MIC of Cu²⁺ were 200.0, 200.0, 450.0, 300.0 and 200.0 mg/L. The maximum Cu²⁺ removal of L1-L5 was achieved at pH 5, 6, 6, 6 and 6, respectively (Fig. 1). The biosorption of Cu²⁺ due primarily to cell-surface binding and their adsorption courses met pseudo-second-order kinetic (Fig. 2). Their adsorption equilibriums of Cu²⁺ fitted the Langmuir model better than the Freundlich model (Table 1). L2, L3 and L4 had better Cu²⁺ adsorption and tolerance capacity than others. Maximal COD removal rates for L2 (77.9%), L3 (68.0%) and L4 (79.0%) were observed at pH 6, 7 and 7, respectively. Obvious COD removal rates decrease happened when the Cu²⁺ concentration reached to 3.0, 5.0 and 10.0 mg/L. L2, L3 and L4 were selected to construct the microbial consortia with the volume ratio was 1:1:1. The dosage was 400.0 mg dry cell/L.

After one-time and repeated batch bioaugmentation, the average COD removal rates reached to 69.0±2.0% and 76.2±2.6% (Fig. 3). Repeated-batch bioaugmentation was more suitable for the bioremediation of seriously deteriorated biological treatment system. The addition of microbial consortia altered the microbial community structure by changing the species evenness and diversity of microorganisms, and establishing a new microbial community balance in situ (Fig. 4). L2 can survive and proliferate to a high and stable quantity, but fungi L3 and L4 cannot become dominant communities and live in the reactor for a long time.

REFERENCES:

[1] J. Fan, T. O. Okyay and D. F. Rodrigues, “The synergism of temperature, pH and growth phases on heavy metal biosorption by two environmental isolates,” J. Hazard. Mater. 2014, 279, 236-243.

[2] E. Mejias Carpio, G. Machado-Santelli, S. Kazumi Sakata, S. S. Ferreira Filho and D. F. Rodrigues, “Copper removal using a heavy-metal resistant microbial consortium in a fixed-bed reactor,” Water Res. 2014, 62, 156-166.

[3] Monchy, M. A. Benotmane, P. Janssen, T. Vallaeys, S. Taghavi, D. Van der lelie, and M. Mergeay, “Plasmids pMOL28 and pMOL30 of Cupriavidus metallidurans are specialized in the maximal viable response to heavy metals,” J. Bacteriol. 2007, 189, 7417-7425.