Pilot scale evaluation of anaerobic codigestion of primary and pretreated waste activated sludge

Abstract

Pilot‐scale (160 L) research on enhancement of anaerobic codigestion of combined primary sludge and waste activated sludge (WAS) was performed, using low‐level alkaline solubilization of waste activated sludge. Solubilization was performed by the addition of 15 meq/L of calcium hydroxide or sodium hydroxide in the first part of the research (data already published), followed by the addition of 15.0, 12.5, or 10.0 meq/L of only sodium hydroxide in the next phase; mechanical anoxic mixing times of 5, 4, and 3 hours were employed. The previous work examined the effects of decreasing solids retention time (SRT) on digester operational efficiency; the subsequent research work examined the effects of different sodium hydroxide dosages and mixing times on digester efficiency. The overall performance of three pilot‐scale digesters, including a control unit, was monitored. This research showed that solubilization of WAS did not have any appreciable effect on actual digester volatile mass reduction efficiency. However, better overall volatile mass reduction (solubilization process plus anaerobic digestion) was achieved in the chemically altered units. Better chemical oxygen demand (COD) removal was also observed in these units. Solubilization of WAS with sodium hydroxide also improved unit gas production (volume of gas produced per volatile mass removed in the digester). Overall, the experimental unit receiving WAS pretreated with different dosages of sodium hydroxide outperformed both the control and the other unit using calcium hydroxide (from previous work) as the solubilizing chemical. Waste activated sludge pretreatment allowed a decrease in digester SRT from 25 to 10 days, without major effects on process efficiency or effluent quality. It enhanced volatile mass reduction, COD removal, and unit gas production.

Effect of SRT on the Anaerobic Digestion of Excess Municipal Sludge

“…(Weemaes et al, 2000) An important factor in the efficiency of the anaerobic digestion is the composition of the sludge. Several authors have reported that waste activated sludge presents higher resistance to digestion due to the fact that it is mostly composed of microbial cells (Shimizu et al, 1993, Knezevic et al, 1995, Tanaka et al, 1997Tiehm et al, 1997;Marjoleine et al, 1998 andWeemaes et al, 2000). The degradable material is confined within a cell wall.…”

Advancement in biogas production from the solid waste by optimizing the anaerobic digestion

“…The chemical pretreatment of feedstock with NaOH increased methane production, but no major change in volatile suspended solids was observed [76]. Biogas production increased ~ 25%, CH 4 production increased ~ 50% and reduction in volatile suspended solids to ~ 60% was observed on pretreatment of the feedstock materials with NaOH at 403 K [74,77].…”

Biogas Plasticization Coupled Anaerobic Digestion: Continuous Flow Anaerobic Pump Test Results

“…Equations 5 and 6 contains α that is the recycle ratio (Q R /Q). Equation 6 relates the cell mass concentration (X) with the substrate utilization and recycle ratio (α) for the Contois function. Substitute α for the (1+α) term in Eqs.…”

“…A coupled continuous AD-conditioning system that could simultaneously lower the refractory coefficient (R→0), such that biodegradable COD S bo →S To as B→B o →0.35 l STP methane (gram total COD (TCOD) fed) −1 , would greatly improve AD use for alternative energy production purposes. Past researchers have investigated a variety of thermal, mechanical, chemical [6], and bioaugmentation pretreatment conditioning methods to improve sludge biodegradability [7]. Heating the mass with steam at 170°C, at 10 atm for 30 min [8][9][10][11] before AD can achieve approximately 10-20% improvement in hydrolysis of solid polymers to an assortment of soluble polypeptides, ammonia, volatile acids, and carbohydrates.…”