Education & Training

Studies on Development and Application of Highly Efficient Complex Microbial Preparation for Organic Pollutants of Composite Tannery Wastewater Treatment

Update time: 07/15/2010

Tanning is second to paper industry in water-consumption and pollution of all light industries. As of late 2007, totaling 7.12×1010 m2 of leather products were processed in China, accompanying with the most conservative estimated 1.15×1010 t of wastewater discharging.  And ambient river heads had been polluted greatly. Biotreatment for tannery wastewater could not operate efficiently because of the following characteristics of wastewater such as: great changes of water quality and quantity, high concentrations of pollutants and large amounts of toxic chemicals and inorganic salt. Therefore, the Chemical Oxygen Demand (COD) of effluent could not stably meet related standard of the 1st level requirements of Integrated Wastewater Discharge Standard (GB8978-1996) sustainingly. The purpose of the thesis is to develop highly efficient complex microbial preparation which targeting on organic pollutants and explore its application, in hope of producing microbial preparation to achieve the high efficient operating of bioaugmentation treatment for composite tannery wastewater.

The optimal ratio of highly efficient strains selected based on analysis of organic components  in composite tannery wastewater was determined by orthogonal experiment. Two highly efficient strains selected for composite wastewater were Tt1 and TZ3. Four highly efficient strains selected for greasing agents were Tt2, Tt1, TW and TZ1. One highly efficient strain selected for degreasing agents was Tt3. 

Two impacts, changing of substrate environment and interactions between strains, resulted in acute fluctuations of strains’ degradation effects along with timing. Therefore, instead of adopting traditionally orthogonal experiment which sampling at a single specific time, orthogonal experiment which continual sampling at different times was introduced to solve this problem. Not only changes of strains’ treatment effects throughout the whole process could be determined thus the adding levels of the best treating effects could be picked out, but also the differences of each strain’s growth and interaction could be balanced and the adding levels of the maximum overall efficiency could been picked out as well as corresponding treating time. 

Best ratio of highly efficient microbial preparation for greasing agents (GrA) was determined, Tt2: Tt1: TW: TZ1= 2: 2: 1: 3, by continual sampling orthogonal experiment. Shaker test of highly efficient complex microbial preparation for composite wastewater showed that the best degradation effect was achieved while culture time was 12 hours and the degradation rate was 68.71%. However, the degradation rate of control group at 12 hour was 12.97%. And the corresponding ratio was Tt3: GrA: Tt1: TZ3= 3: 2: 3: 2.

The next step after determination of best ratio was large scale application of complex microbial preparation. This could be achieved by mixed microbial fermentation, which could obtain large amounts of highly efficient strains rapidly. However, the exact ratio of each strain after mixed fermentation was hard to determine because microorganisms were of small volume, hard to be distinguished and proned to aggregate. Therefore, related explores on quick   measurements of strains’ concentrations in a mixed system had been carried out. Based on multiwavelength method, optimizational concentrations of 6 different strains in a mixed system could be calculated by regressing absorbancies at 12 specific wavelengths with Least-absolute-residuals, of which average error was 5.3%. Problem of inaccuracy resulting from interferences of traditional multiwavelength method that choosing absorbancies at only 6 specific wavelengths to obtain 6 strains’ concentrations in the same mixed system was tackled, of which average error was 67.7%.

Bioaugmentation treatment effect of highly efficient complex microbial preparation was tested by SBBR reactor: while the Hydraulic Retention Time (HRT) was 12 hours, the average COD of treatment group was 78.47 mg/L, meeting related standard of the 1st level requirements of GB8978-1996 and the rate of meeting the 1st level requirements was 91.80% within 61 operation periods; while the HRT was 12 hours, the average COD of control group was 135.60 mg/L, just meeting related standard of the 2nd level requirements of GB8978-1996 and the rate of meeting the 1st level requirements was only 9.84% within 61 operation periods.

Experiments showed that the former problems of biotreatment for composite tannery wastewater, such as hard to operate efficiently and stably, could be solved by bioaugmentation  technology which adding highly efficient complex microbial preparation, making COD of  effluent meeting the 1st level requirements of GB8978-1996. This study could provide  references on the development and application of related microbial preparations.

Keywords: bioaugmentation; composite tannery wastewater; continual sampling orthogonal experiment; complex microbial preparation; multiwavelength method; Least-absolute-residuals