| Containing massive complex organics, heavy metals and other harmful substances, pharmaceutical sludge has to be treated as the hazardous waste. To reduce the treatment and disposal cost, the surplus sludge volume is required to be reduced at source. The efficienc is low when sludge is direct digested, while the sludge can be effectively digested through ozone oxidation pre-treatment. This paper studied the effect of pre-treatment with different initial sludge concentration, ozone concentration and ozone dosage, and then investigated the effect of sludge digestion with different dosing rates after the pre-treatment, as well as the changes in concentration of organics and heavy metals in the sludge during the process of ozone oxidation pre-treatment. The main conclusions are as follows:1. With the fixed initial sludge concentration and ozone concentration, and within certain range of ozone dosage, sludge mixed liquor TSS, VSS, SCOD, TCOD and TP increased linearly with time; with high ozone concentration, the slope of this straight line became big with rapid cell lysis. When exceeding the range of ozone dosage, TSS, VSS, SCOD, TCOD and TP changed slowly with slower cell lysis. The lysis rate and ozone dosage were used as the evaluation indexes to investigate the pre-treatment efficiency. With high ozone concentration, the lysis rate was high while lower than ozone dosage, and ozone concentration could be 56mg·L-1; with the fixed ozone concentration, ozone consumption has no relation to the initial sludge concentration; the higher initial sludge concentration and ozone concentration should be selected to reduce the reactor volume and shorten the pre-treatment time. With the ozone concentration of 80mg·L-1, initial sludge concentration of 31.9g·L-1, and ozone dosage of 56 mg O3·（g TSS）-1, TSS and VSS decreased by 49% and 57% respectively during the pre-treatment, SCOD, TCOD and TP respectively increased from 1,219 mg·L-1, 1,819 mg·L-1 and 40.7 mg·L-1 to 6,319 mg·L-1, 17,429 mg·L-1 and 204.4 mg·L-1, the average particle size of sludge decreased from 420μm to 239μm, SV30 turned 95%, and the sludge settleability became poor.2. After the ozone pre-treatment, the removal rate of TSS and VSS by anaerobic digestion and biogas production increased, e.g., with the dosing rates of 5%, 8% and 10%, the removal rate of TSS increased from 37.2%, 29.1% and 22.0% to 46.8%, 40.1% and 38.0%; the removal rate of VSS increased from 43.5%, 37.0% and 30.6% to 50.3%, 41.1% and 41.5%; and biogas generation rate increased by 52%, 29% and 18% respectively. After the digestion, standardized CST decreased and the sludge filtration was improved.3. The comprehensive toxicity of organics in the sludge was characterized by acute biological toxicity. After the ozone oxidation pre-treatment, the light inhibition of sludge reduced from 88% to 43%, the status became poisoning from high toxicity; after the anaerobic digestion and aerobic digestion, the status became poisoning and low toxicity. The analysis of heavy metal content showed that: copper and nickel were the main pollutants. Through analyzing the characteristic organics in sludge, this paper found that the removal rate of PAHs, PCBs, hexacosanol, semicarbazide, creatinine and piperidine by ozone oxidation pre-treatment was 43.9%, 24.2%, 20.4% and 93.2%, 72.2% and 81.2%. |
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