Study of different ratios of primary and waste activated sludges to enhance the methane yield

Abstract

This work aimed the study of methane yield using different proportions of primary sludge (PS) and waste activated sludge (WAS) for anaerobic digestion (AD) conversion. Three trials were carried out: T1 (60 : 40, v/v), T2 (80 : 20, v/v) and T3 (100 : 00, v/v) to estimate the best proportion in comparison with a reference scenario, T0 (40 : 60, v/v). AD was performed in mesophilic conditions with a hydraulic retention time (HRT) of 15 days and an organic loading rate (OLR) expressed in total volatile solids (TVS) of 1.62 ± 0.06 kgTVS m−3 day−1. Biogas production for trials T1 and T2 increased from 45 to 71% in comparison with T0. The experimental methane production along trials was used to assess the energy recovery corresponding to increases from 32 to 55%. The most suitable trial to be implemented at real‐scale is T1, applying a lower PS solid retention time combined with an increase of WAS thickening.

Feasibility and potential of separate anaerobic digestion of municipal sewage sludge fractions

“…Sludge that cannot be fed in these incidences returns to the main line and adds to the vicious circle of solids in the plant (Erdirencelebi and Kucukhemek, 2015). An optimum ratio determined for MS at 60(PS):40(SS) (v:v) by Pinto et al (2016) is hardly possible to attain in a routine WWTP operation as PS is drawn on a periodical basis from the primary settling tanks during the daytime. Return SS is formed at varying solid content, depending on the settling degree in the secondary settling tanks, and pumped at varying flowrates to ensure the design biomass concentration and sludge age in the biological treatment unit.…”

Production Of Value-Added Products From Waste Derived Volatile Fatty Acids: A Review

“…There are some optimization factors that can be considered. As shown in the study by Pinto, et al (2016), there is an optimal mixture which may sometimes be obtained between different waste types. WAS and PS are two of the most available waste types.…”

“…This may include wastes from kitchen, toilets, vegetables, fruits and more (Ji, et al, 2010). On the other hand, waste activated sludge is generated in the biological treatment of a wastewater treatment plant and may consist of non-hydrolysable particulate materials that have been broken down due to biological metabolism (Pinto, et al, 2016). Mixed sludge is a combination of the primary sludge and waste activated sludge.…”

“…Often, mixed sludge is a prominent source for VFA production, as it is rich in organic matter from the primary and waste activated sludge. The downside to this is that the mixed sludge contains much more insoluble chemical oxygen demand (COD) than soluble COD, leading to longer retention times as hydrolysis cannot be achieved as quickly as desired (Pinto, et al, 2016). Pretreatment is a possible solution to this but will drive up the cost to run the anaerobic digester.…”

Energetic Valorization of Cereal and Exhausted Coffee Wastes Through Anaerobic Co-digestion With Pig Slurry

“…The operational parametersorganic loading rate (OLR), biogas production rate (GPR), methane production rate (MPR), specific methane production (SMP), and specific energy loading rate (SELR)-were determined twice per cycle. The specific energy loading rate (SELR, gCOD d −1 gVSS −1 ) refers to the ratio between the daily average fed organic load (expressed in TCOD) and the active biomass inside the reactor (expressed in TVSS) (Pinto et al, 2016), related to the methanogenic activity. The Equation (1) illustrates this relationship.…”