Performance and methane potential of up-flow anaerobic sludge blanket treating thermal hydrolyzed sludge dewatering liquor.

Thermal hydrolysis pretreatment could release organic sufficiently from solid into liquid phase to accelerate the high solid sludge anaerobic digestion. Thus, up-flow anaerobic sludge blanket (UASB) could be a promising energy recovery process to treat thermal hydrolyzed sludge dewatering liquor with significantly augmented the organic loading rate (OLR). In this study, its performance was investigated using a lab-scale UASB to treat sludge dewatering liquor after 165 °C, 30 min thermal hydrolysis pretreatment. The results show that 85.57% of the organic in thermal hydrolyzed sludge dewatering liquor could be converted to methane. The UASB adapts to high OLR stably, and the COD removal efficiency was 71.98 ± 1.95% at OLR of 18.35 ± 0.78 kgCOD·(m3·d)-1, and the gap between the maximum potential and experimental methane production yields could be observed during different OLRs. It could be explained as the methanogenesis rate decreased due to the shift of dominant pathway from acetoclastic methanogenesis to syntrophic acetate oxidation following hydrogenotrophic methanogenesis. Methanospirillum became the dominant methanogen with the increase of OLR. In addition, the methane production yield and rate would be hindered till the ammonia nitrogen concentration exceeds 4 g·L-1. Direct interspecies electron transfer could be promising methods to improve UASB performance treating thermal hydrolyzed dewatering liquor.

Accelerated stabilization of high solid sludge by thermal hydrolysis pretreatment in autothermal thermophilic aerobic digestion (ATAD) process.

Autothermal thermophilic aerobic digestion (ATAD) is a rapid biological treatment technology for sludge stabilization. To improve digestion efficiency and shorten stabilization time, thermal hydrolysis pretreatment was employed before ATAD of high solid sludge. The results showed that accelerated stabilization of high solid sludge (total solid = 10.1%) was achieved by thermal hydrolysis pretreatment with volatile solid removal efficiency of 40.3% after 8 days of ATAD, 11 days earlier than unpretreated sludge. The enhanced release and hydrolysis of intracellular organics resulted in a solubilization degree of 45.3%. The reduced sludge viscosity and improved fluidity after thermal hydrolysis facilitated mixing, aeration and organics degradation during ATAD. Excitation emission matrix analysis indicated that the fluorescence intensity of soluble microbial byproduct and tyrosine-like protein increased markedly after thermal hydrolysis and decreased after ATAD. The proportion of high molecular weight (MW > 10 kDa) substances in the supernatant increased significantly after thermal hydrolysis, while the low MW (MW < 1 kDa) substances decreased after ATAD. The significant difference in microbial composition between the pretreatment and control groups elucidated the accelerated sludge stabilization under thermal hydrolysis. This work provides an efficient and practical strategy to achieve rapid stabilization of high solid sludge.

Viability of recuperative thickening in upgrading thermophilic and mesophilic anaerobic digestion of hydrothermal high-solid sludge.

Recuperative thickening (RT) process was introduced to further upgrade anaerobic digestion of hydrothermal high-solid sludge. Continuous mesophilic (MD-R) and thermophilic (TD-R) digestion with RT (MD-R) were operated synchronously, with corresponding single digestion without RT as controls, namely MD and TD. The MD-R and TD-R increased biogas production rates by 22.8% and 11.0%, and achieved 16.6% and 9.7% higher volatile solids reductions, respectively. The improved performance was partly attributed to increased hydrolysis rate, with 11.2% and 7.4% higher for the MD-R and TD-R than the controls, respectively. The RT increased the numbers of total archaea in the mesophilic and thermophilic systems by 844% and 108%, and the numbers of dominant archaea by 50.4% and 38.1%, respectively, which promoted the degradation of organic matter and the production of biogas. Thus, RT is applicable to further upgrade digesting high-solid sludge.

Optimization of hydrothermal pretreatment conditions for mesophilic and thermophilic anaerobic digestion of high-solid sludge.

Hydrothermal pretreatment (HTP) conditions were optimized for continuous mesophilic (MAD) and thermophilic (TAD) anaerobic digestion of high-solid sludge (10-11% total solids). COD solubilization increased with prolonged HTP durations, and became not significant after 210 min. According to the methane production rate and energy consumption, the optimal HTP temperature was determined at 160 °C. Regarding continuous operation without HTP, TAD achieved higher methane yield and volatile solids (VS) reduction, at 0.12 L/g VSadded and 23.9%, respectively. After HTP, methane yield and VS reduction in MAD and TAD were increased by 400% and 191% (MAD), 67% and 72% (TAD), respectively. TAD was limited due to the inhibition from about 2800 mg/L of NH4+-N concentration. The methanogenic activity of MAD was enhanced, whereas TAD displayed a reduced value owing to ammonia inhibition. Ultimately, MAD with HTP and TAD without HTP achieved the higher energy balance, 5.25 and 3.27 kJ/g VS, respectively.

The transformation of phosphorus fractions in high-solid sludge by anaerobic digestion combined with the high temperature thermal hydrolysis process.

Transforming inactive phosphorus (P) to active P to recover it from waste activated sludge is important. The transformation of P fractions from high-solid sludge by the anaerobic digestion (AD) and acidification phase of AD (AAD) combined with a high temperature thermal hydrolysis process (HTTHP) was investigated. The results showed that the sequence of P release effects by three processes was HTTHP + AAD > AD + HTTHP > HTTHP + AD. The PO43--P release from high-solid sludge was directly affected by the temperature of HTTHP. At 140 °C, each process had more PO43--P release than that at 160 °C. The total amount of PO43--P release in AD + HTTHP was approximately 6 times that of HTTHP + AD. Based on the experimental results, a new process of mesophilic AD - post HTTHP was recommended, in which, enhancement of P release by sulfide ions was also proposed.

[Influence on Desulfurization Efficiency and Interactions of Fe/S and pH During H2S in situ Depression of High Solid Anaerobic Digestion].

To evaluate the influence of Fe/S ratio and pH on sulfide removal efficiency and interactions between Fe/S and pH, anaerobic hydrogen sulfide in situ depression tests and digested sludge liquor sulfide removal tests were carried out by using dewatering sludge from a wastewater treatment plant (WWTP). Results showed that the concentration of hydrogen sulfide in biogas from the thermal pretreatment following anaerobic digestion process could be reduced from 170.4×10-6 to 14.09×10-6 at Fe/S=7.75, which means the biogas desulfurization treatment is not required. Under the condition of pH 7.00-7.50 and Fe/S 1-11, pH is the main influencing factor for sulfide removal. Improving the pH of anaerobic digestion is beneficial in reducing the dosage of Fe(Ⅲ). An Fe/S ratio of 7.0 is the minimum to meet the biogas hydrogen sulfide emission standards during high solid sludge anaerobic digestion. The concentration of hydrogen sulfide was not up to standards if pH was below 7.30.

Influence of thermal hydrolysis pretreatment on organic transformation characteristics of high solid anaerobic digestion.

The study evaluated the influence of thermal hydrolysis pretreatment (THP) on anaerobic digestion (AD) ability of high solid sludge. The transformation characteristics of organics during the THP+AD process of dewatering sludge from wastewater treatment plant was investigated using a lab-scale THP reactor and four anaerobic digesters. The reduction efficiency of volatile suspended solids using THP+AD exceeded 49%. The acceleration of biogas production during AD was due to the enhancement of protein hydrolysis and acidogenesis by THP. THP had only minimal influence on the improvement of carbohydrate acidogenesis. The hydrolysis of poly phosphates was likely the main reaction of phosphorus transformation. Biochemical generation of sulfide and ammonia nitrogen occurred during the acidogenesis.

Modified ADM1 for modeling free ammonia inhibition in anaerobic acidogenic fermentation with high-solid sludge.

Anaerobic acidogenic fermentation with high-solid sludge is a promising method for volatile fatty acid (VFA) production to realize resource recovery. In this study, to model inhibition by free ammonia in high-solid sludge fermentation, the anaerobic digestion model No. 1 (ADM1) was modified to simulate the VFA generation in batch, semi-continuous and full scale sludge. The ADM1 was operated on the platform AQUASIM 2.0. Three kinds of inhibition forms, e.g., simple inhibition, Monod and non-inhibition forms, were integrated into the ADM1 and tested with the real experimental data for batch and semi-continuous fermentation, respectively. The improved particle swarm optimization technique was used for kinetic parameter estimation using the software MATLAB 7.0. In the modified ADM1, the Ks of acetate is 0.025, the km,ac is 12.51, and the KI_NH3 is 0.02, respectively. The results showed that the simple inhibition model could simulate the VFA generation accurately while the Monod model was the better inhibition kinetics form in semi-continuous fermentation at pH10.0. Finally, the modified ADM1 could successfully describe the VFA generation and ammonia accumulation in a 30m3 full-scale sludge fermentation reactor, indicating that the developed model can be applicable in high-solid sludge anaerobic fermentation.