Transformation Characteristic And Treatment Of Nitrogen And Sulfur During Thermal Hydrolysis Pretreatment Followed By High Solid Anaerobic Digestion Of Wasted Activated Sludge And Biogas Desulfurization

With the gradually application of high solid thermal hydrolysis pretreatment?THP?followed by anaerobic digestion?AD?in wastewater treatment plants?WWTPs?sludge treatment,the nitrogen and sulfur transformation characteristic remained unclear.The mechanism analysis of H₂S decrease during high solid AD?HSAD?is beneficial to reduce the cost of biogas desulfurization.Thus,an in-depth understood of the transformation characteristic and control of nitrogen and sulfur during high solid THP-AD during WAS high solid THP-AD process and biogas desulfurization,could provide technical support for decreasing the WAS treatment cost and the resource reuse of WAS.Firstly,the characteristic of ammonia nitrogen generation during high solid THP-AD process was investigated.Meanwhile,the reasons of H₂S concentration decrease during HSAD were discussed.Moreover,the feasibility of ammonia pre-separation during the high solid thermal-alkaline pretreatment?TAP?with exhausted gas released of WAS was evaluated by analyzing the variations of nitrogen compositions and organic concentrations during pretreatment.At last,the biodesulfurization characteristics of the low H₂S concentration biogas were investigated by using a lab-scale external aeration biotrickling filter?BTF?.An in-depth analysis of the variations of H₂S and DO concentration were conducted by the continuously tests and establishing a counter-current one-demisional multi-layer BTF model.The main conclusions are as following.The characteristic of nitrogen transformation during high solid THP-AD process was investigated by the batch tests and continuously tests.While the organic hydrolysis ratio could reach as high as 40%,the ratio of ammonia nitrogen to total nitrogen was 20%under THP condition of 165?and 12.5%solid content.And,the ammonia nitrogen in WAS was produced mainly in AD?approximately 65%?and secondarily in THP?approximately 35%?under THP condition of 165?and 10%solid content.The results of continuously anaerobic acidogenesis tests?HRT:2-5d?of pretreated WAS indicated that the ammonia nitrogen was mainly produced in acidogenesis process.And the biochemical generation of ammonia nitrogen during anaerobic acidogenesis is prior to sulphide.The approach of mitigating ammonia inhibition in digester during high solid THP-AD is to control the ammonia nitrogen concentration after THP.The feasibility of improving HSAD performance of WAS and separation ammonia nitrogen by TAP was evaluated by batch tests.Under condition of 120?,30-150min,0.05-0.20gCaO/gTS and 12.5%solid content,the VSS hydrolysis ratio could reach as high as 43.45%,and the lime dosage could accelerate organic hydrolysis rate by 59.07-73.18%.Thus,the integration of high solid TAP and HSAD could increase the sludge loads at a lower pretreatment temperature.Meanwhile,1.40±0.68g/L of ammonia nitrogen was produced during high solid TAP,and ammonia nitrogen could be effectively separated from the sludge.Therefore,the high solid TAP provides an alternative approach to recover nitrogen in the WAS.AD batch tests of conventional and high solid?20days,36±1?,120rpm?were conducted to evaluate the influence of ammonia nitrogen on sulphide production during AD.The results of AD batch tests showed that increase of ammonia nitrogen in digester leads to the decrease of H₂S concentration during HSAD.The anaerobic biodegradation microorganism of cysteine and methionine were enriched by using continuously mesophilic acidogenesis tests?pH=6.02±0.40?.The results showed that the sulphide could be produced during the biodegradation of cysteine,and there was almost no sulphide detected during methionine biodegradation.Thus,the sulphide production during methionine biodegradation is related to hydrolysis bacteria and methanogens.Biodesulfurization characteristics of the lab-scale external aeration BTF was investigated by continuously test.Under condition of inlet H₂S concentration 200ppmv,empty bed retention time?EBRT?40-100s,gas to liquid flow ratio?G/L?2-5 and pH value7.0-9.0,the H₂S removal efficiencies were 92.27±10.30%.Under condition of the pH value exceeded 8.0,95.63%of the outlet H₂S concentration measurements meets its standard in China?GB17820-2012,Class II?.Meanwhile,72.23±26.52%of H₂S were removed from the 50%of the packing volume.Single-factor tests?DO 0.25-5.0mg/L?were conducted to analysis the influence of DO concentration on H₂S removal efficiency,and the results showed that the DO concentration should exceed 1.0mg/L to decrease its negative influence on desulfurization efficiency.A one-dimensional multi-layer counter-current BTF model was established and calibrated based on flow state of BTF and metabolic properties of sulfur-oxidation bacteria?SOB?.The outlet H₂S concentration?R²=0.9146?and H₂S vertical differences?R²=0.9120?in the packed bed could be accurately predicted by the model simulation.By analyzed the simulation results of the H₂S distribution in the packed bed,the low H₂S concentration biogas desulfurization process was mainly influenced by non-biological stage at low pH value or biological stage at high pH value,respectively.According to the value of the sulphide affinity constant,the sulfur-oxidation bacteria presents low affinity to sulphide during the biodesulfurization process of the biogas with low H₂S concentration.Therefore,the sulfur load rate of BTF is hindered by the sulphide affinity of SOB.