Effect of low-thermal pretreatment on the methanogenic performance and microbiome population of continuous high-solid anaerobic digester treating dewatered sludge.

Undigested and dewatered sludge at 10% total solids was pretreated at 60 °C for 3 h and fed to a lab-scale horizontal anaerobic bioreactor for 130 days with solids retention time (SRTs) from 25 to 16 d. The low-thermal pretreatment enabled higher net energy production, improved sludge treatment efficiency, and enhanced digestion stability. The highest average biomethane yield and production rate were 138.5 mL/g VS and 0.43 L/L.d, respectively, and the economic benefit was expected to be the maximum at SRT 16 d. Pretreatment did not increase the specific methanogenic activity per unit methanogen, but resulted in higher abundance of methanogenic archaea and hydrolytic bacteria. Methanogenic population shifted from hydrogenotrophic to acetoclastic, consistent with predicted gene expression at SRT equal or below 20 d. Anaerobic digestion along with low-thermal could be a feasible management strategy for undigested dewatered sludge from small WWTPs.

Density profile modeling for real-time estimation of liquid level in anaerobic digester using multiple pressure meters.

The liquid level of a bioreactor is an important operating parameter governing the hydraulic retention time. In this study, a novel method is proposed to estimate the liquid level of anaerobic digesters. The proposed method has an advantage over typical differential pressure measurement as it considers the heterogeneity of the digestate along the level using multiple pressure meters. The real-time measurement generates a model to fit the densities at different liquid columns, predicts the density of the surface layer and determines the overall liquid level. A pilot-scale (0.33 m3 working volume; 1.2 m liquid level) digester, equipped with seven pressure meters, was operated to test the methodology. The performance of the digester was confirmed stable during a long-term (175 d) operation. A set of density-pressure models was developed and were validated using the long-term experimental data. The new method employing cubic model showed significantly better estimation of the reactor level (mean error rate of 1.31%) with improved CDF, as compared with the traditional differential pressure method (mean error rate of 5.71%). The methodology proposed in this study is simple, robust, and cost-effective and can be used to provide additional insights into the operation of an anaerobic digester such as assessing the mixing efficiency.

Influence of thermal hydrolysis pretreatment on physicochemical properties and anaerobic biodegradability of waste activated sludge with different solids content.

The influence of thermal hydrolysis pretreatment (THP) on physicochemical properties (pH, total solids, volatile solids, chemical oxygen demand, total nitrogen, ammonium nitrogen, volatile fatty acids, viscosity, and cell morphology) and anaerobic biodegradability of highly concentrated waste activated sludge (WAS) with TS content ranging from 1 to 7% was evaluated at different temperatures ranging from 100 to 220 °C. The biomethane potential (BMP) of the WAS was systematically analyzed and evaluated. Images of its cellular structure were also analyzed. The results indicated that THP is a useful method for solubilizing volatile solids and enhancing CH4 production regardless of the TS content of the WAS feed. The ultimate CH4 production determined from the BMP analysis was 313-348 L CH4/kg VS (72.6-74.1% CH4) at the optimum THP temperature of 180 °C. The results showed that THP could improve both the capacity and efficiency of anaerobic digestion, even at a high TS content, and could achieve the dual purpose of sludge reduction and higher energy recovery.