Research On Sludge Deep Dewatering Technology And Safety Evaluation Based On CFD Numerical Simulation

Sewage treatment process produced a large number of sludge with high moisture content and huge volume.Deep dewatering technology of sludge can effectively reduce the water content of sludge,which was of great significance for sludge reduction.This paper was based on the advantages of CFD numerical simulation technology in the simulation of fluid condition.An aerated reactor with a daily handling capacity of 1 tons was constructed by using an acidophilic iron oxidizing characteristic of Acidithiobacillus ferrooxidans XJF8.A pilot scale experiment of sludge dewatering in field demonstration was conducted.The sludge dewatering process of safety evaluation was operated in the end,the following results were obtained:The process of gas-liquid?slurry?two-phase flow in airlift reactor was simulated by Fluent software.The variation of flow field in the reactor with different liquid medium and ventilation rate was investigated.The analysis of the simulation results showed that:1)The liquid medium in the reactor was the flow field?gas hold-up,liquid velocity and turbulent intensity?of slurry,which was lower than that of water;2)When the liquid medium is slurry,with the increase of ventilation volume,the reactor operating conditions are as follows:the liquid velocity and gas hold-up at the bottom of reactor increased;the gas hold-up in the upper part of reactor increased first and then dropped,and the liquid velocity and turbulent intensity increased continuously.2)when the liquid phase medium was mud,the best ventilation rate of the sludge deep dewatering process reactor was recommended to use 0.10vvm.The biological conditioning degree and dehydration effect of sludge under different ventilation volume were studied by batch experiment.Based on the numerical simulation of aeration,the sludge solids content,Fe²⁺oxidation rate,dissolved oxygen and sludge specific resistance in different locations of reactor were investigated,the following conclusions are obtained:1)the influence of aeration on sludge solids content in reactor is mainly at the bottom.Ventilation 0.04vvm,reactor operation to second days,fixed rate from 2.04%to 11.23%with the bottom of the sludge,and the solid content of the sludge is 2.04%-2.81%in the upper part of the reactor;when ventilation was 0.06vvm-0.12vvm,the time of the solid content of the sludge is longer than that of 0.04vvm,it taked 3 days,and the longer the ventilation was,the longer it was up to this solid rate,the solid content of the sludge in the upper part of the reactor was stable at 2.73%.This was in agreement with the conclusion of the flow field in the numerical simulation reactor.2)The critical value of ventilation for the optimal treatment is0.06vvm.The oxidation rate of Fe²⁺ions,the dissolved oxygen and the specific resistance of sludge under the different ventilatory volume and different positions were compared.When the aeration rate was 0.04vvm,the sludge conditioning lasted for third days.The Fe²⁺oxidation rate of the upper part of the reactor was only 80.12%,the dissolved oxygen content was2.31mg/L,the sludge specific resistance was 1.32×1012 m/kg,which belonged to the refractory sludge.When the aeration rate was 0.06vvm,the sludge conditioning lasted for third days.The Fe²⁺oxidation rate of the upper part of the reactor was 99.5%,the dissolved oxygen content was 3.12mg/L,the sludge specific resistance was 0.47×10¹² m/kg,which belonged to easy dewatering sludge.The parameters of the air lift reactor were further optimized by continuous flow experiment.When the ventilatory volume was 0.06vvm,the study found that the sludge retention time of 2.5d,sludge return ratio of 80%,when the dosage was less than 0.40g/L,the sludge specific resistance of the treated sludge is 5.41×10¹²m/kg,which belonged to the refractory sludge;when the dosage was 0.45g/L,sludge return ratio of 80%,sludge retention time of 1.5d,the sludge specific resistance of the treated sludge is 5.41×10¹²m/kg,which belonged to the refractory sludge.When the dosage was 0.45g/L,the sludge retention time of1.8d,sludge return ratio of 80%,the sludge specific resistance of the treated sludge is reduced to 0.58×10¹²m/kg<1×10¹²m/kg,which belonged to the easily dewatered sludge.The optimum operating parameters of the reactor were obtained:the dosage of 0.45g/L,the sludge retention time of 1.8d,and the ventilatory volume of 0.06vvm.Under the condition of no cationic polyacrylamide?CPAM?and continuous running of 12d,the water content of the sludge is lower to 50%at this parameter after filter press filter press filter press filter press filter.Deep dewatering of sludge had been realized.The structure of the sludge deep dewatering process system and the hidden danger of the process system are qualitatively analyzed.The effects of the risk factors of the sludge deep dewatering process on the safe operation of the system are quantitatively analyzed,the depth of biological sludge dehydration process preliminary hazard risk assessment table was established.The precautions against the risk factors of the system were put forward to provide scientific basis for the stability and safety of the sludge deep dewatering process system.