Research On Anaerobic Digestion Of Pretreated High Solid Concentration Sludge

The advantages of anaerobic digestion of high solid concentration sludge which can use the dewatered sludge directly,include low energy consumption,small reactor size and high volume biogas production.However,because of the high solid concentration and viscosity,there are some problems of stirring difficult y,easier accumulation of ammonia and VFAs,low removal rates of organic matter and methane yield.Co-digestion with food waste and pretreatment are effective ways to improve the biogas yield of sole sludge digestion.In this study,effects of co-digestion and pretreatment on sewage sludge with a total solid concentration(TS)of 8% were investigated.On the co-digestion aspect,effects of addition of food waste on high-solid sludge anaerobic digestion were investigated in batch experiments.Methane production,methane yield and VS removal efficiency were examined to select an optimal mixing ratio of sewage sludge and food waste.Results showed the optimal TS ratio between sewage sludge and food waste was 4:1,with a methane yield of 122.4mL/g-VSadd and VS removal efficiency of 47.9%,which were 39.1% and 18.0% higher than those of sole sludge digestion,respectively.Then the CSTR was used to investigate co-digestion of sewage sludge and food waste in anaerobic digestion process.Results showed that the methane yield and VS removal efficiency of co-digestion under the TS ratio of 4:1 increased by 2.7~3.5 times and 1 time more than those of sole sludge digestion.When the HRT was shortened from 25 d to 20 d,the pH value fell to around 6.8.And with the increased of organic loading rate(OLR),the methane yield and VS removal efficiency decreased,which due to incomplete degradation of digestion substrates.On the pretreatment aspect,sewage sludge with a TS of 8% was pretreated by alkaline,alkaline plus ultrasonic,and simultaneous alkaline and ultrasonic methods.Effects of different alkali additions and these three pretreatment methods on organic matters dissolvation and biogas production were investigated in batch experiments.Results showed that the pH value,SCOD value and methane yield increased with the increase of alkali dosage.And alkaline pretreatment could shorten the digestion period and make peak value of biogas production appear earlier.At alkali dosage of 0.01g-CaO/g-TS,simultaneous alkaline and ultrasonic pretreatment for 30 min improved methane production obviously,with methane yield increase of 55.13%.Considering the sludge pretreatment efficiency,methane yield,anaerobic digestion stability and economics,the combined alkaline and ultrasonic pretreatment under lower dosage of alkali was more appropriate.At the same time,the result of CSTR experiment showed that the combined alkaline and ultrasonic pretreatment under alkali dosage of 0.01g-CaO/g-TS had better effects on enhancing digestion process,than alkaline pretreatment.Meanwhile,ultrasonic pretreatment could reduce the viscosity of sewage sludge,which was more beneficial to the anaerobic digestion.The results also showed that co-digestion with food waste was more effective on increasing the methane yield of high-solid sludge anaerobic digestion than that of alkaline pretreatment,and as same as that of simultaneous alkaline and ultrasonic method.