| Excess sludge from wastewater treatment plants(WWTPs) is always with heavy production and high disposal cost, p osing serious environmental problems. Therefore, reducing sludge production during wastewater treatment process has important economic and environmental significance. Lysis-cryptic growth wastewater treatment process is one of the most promising technology for excess sludge reduction from the source. However, changes of heavy metals and its effects on wastewater treatment system has not been effectively solved, which posing a security risk on the application of this technology. This work combined ultra sonic sludge lysis process with Sequencing Batch Reactor(SBR) to study the redistribution of heavy metals(HM) between sludge liquid-solid phase and thire chemical fraction changes during lysis process. Mechanisms of heavy metals accumulation on lysis-cryptic growth system were studied at the meanwhile. An organic matters degradation mathematical model on lysis-cryptic growth wastewater treatment process was proposed.Static test were employed for studying the changes of HMs during sludge lysis process. Redistribution of heavy metals(HM) between sludge liquid-solid phase and chemical fraction distribution changes of eight kinds of typical sludge HMs(including As, Zn, Ni, Cd, Cr, Cu, Pb and Hg) were studied during ultrasonic sludge lysis process. The effect o f key parameters for sludge lysis on HM changes were studied. Results showed that ultrasonic lysis could release heavy metals from sludge solid phase into liquid phase, and enhance the stability of HMs in sludge. Sonication time and ultrasonic intensity affected the solid-liquid distribution of HMs. With intensity of 188 W/cm2, the release of HMs was proportional to sonication time at the range of 0-15 min. Effective energy range of 125-251 W/cm2 for HM release was found when sonication time was controlled to 15 min. Chemical fraction distribution of HM in sludge was affected by sonication. The individual characteristics of HMs were another contribution on the change. When fixed power density at 188 W/cm2, the unsteady chemical fractions of HMs decreased wi th sonication time increasing, and changes of steady fractions were on the contrary. Unsteady metal such as As, Zn and Ni in sludge was easy to be affected by sonication, with a higher release and significantly fraction distribution changes. Cu, Pb and Hg were stable and sonication had little effect on them. The chemical fraction distributions change was insignificant. RSM were used for simulating HM release law during sludge lysis process. The total heavy metal release law was a function of sonication time and ultrasonic intensity, which was described as CHM =-3069.09 + 107.49 × t + 27.46 × I + 0.10 × t × I- 2.11 × t2 – 0.06 × I2. The release concentration of HMs were determined by lysis parameters.Contract to traditional SBR system, the sludge reduction and wastewater treatment effects in sludge reduction system were analyzed. Based on the above analysis, accumulation and chemical fraction changes of HMs were emphasized during sludge reduction process. Changes of sludge reduction,effluent quality and sludge activity were studied. Results showed that the daily average sludge production was about 85±12 mg/L/d, cut for 50% sludge growth comparing to the control group. The removal of COD was about 70%. The concentration of NH4+-H in effluent was 16 mg/L. The concentration of total phosphorous increased a bit. Compared to the control system, HMs accumulated at a large amount in sludge reduction system, but affected little on sewage treatment operation. The fa te and chemical fraction changes of each metal were different since the selectively bio-adsorption of activated sludge on HMs.Therefore the removal of each metal was different. The removal of Cu was up to 98%, since electrophilic organic order of Cu was high. Correspondingly, the accumulation of copper was high. The adsorption of Pb and Cd by activated sludge was competitive, and the accumulation law of the m was opposite. Chemical fraction distribution changes of heavy metals in sludge reduction system was related to the adsorption mechanisms by activated sludge. The unsteady fractions of HMs enhanced a bit after 120 days’ operation. Potential ecological risk of sludge heavy metals were analyzed during lysis-cryptic growth wastewater treatment process. Resul ts showed that the potential ecological risk of HMs accumulation(except Cd) on environment remained in a low range. The accumulation of Cd in sludge contained great potential ecological risk and should be got appropriated disposal.PCR-DGGE technology was used to study the microbial community structure of sludge reduction system. Results showed that sludge microbial species in reduction system were more than in the control, and Sphingobacterium;Spirochaeta sp. and Uncultured Acinetobacter sp. were found to be functional bacteria on sludge reduction system.In order to effectively and accurately predict the affect and mechanism of HMs accumulation on the ultrasonic sludge lysis-recirculated SBR wastewater treatment process, A sample mathematical model based on Monod Function including organics degradation and microorganism growth on l ultrasonic sludge lysis-recirculated SBR wastewater treatment process was proposed. This model is greatly simula ted the sewage treatment process. The activated part of sludge decreased and the non-degradable organic particles increased because of the exiting of HMs. The lyzed sludge as a second substrate. involved in the microorganisms metabolism, and F/M increased to 0.93 mg COD/mg biomass/d. The maximum specific growth rate of sludge microorganisms calculated was about 3.27 d-1. The simulated value of effluent COD concentration greatly fit with the actuated value, illustrating that the model was better for predict the ultrasonic sludge lysis-recirculated SBR wastewater treatment process. The influent concentration of HMs affected the degradation of organic matter and excess sludge reduction. The simulated results showed that when the concentration of HMs was at the range of 5-12.5 mg/L, COD removal was 62.5%-80% and the sludge observed yield coefficient was 0.26-0.41 mg MLSS/mg COD. |
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