Abstract
This study evaluated the effects of sodium on anaerobic biomass from the second-stage reactor of a two-stage anaerobic digester. The results indicated that methanogens showed a relatively high sodium tolerance of 2.4 g Na+ L−1. Microbial community analysis showed that viable Methanomicrobiales was the most abundant population by a combined propidium monoazide cross-linking quantitative polymerase chain reaction technique. There was a population shift towards higher abundance of Thermotoga (0.02%), Clostridium (2.50%) and Methanoculleus (13.80%). Biomass activity in relation to increased sodium concentrations was investigated with the adenosine triphosphate test coupled with extracellular polymeric substances measurement. The results showed biomass activity decreased from 33 to 16 µg g−1 volatile suspended solids as sodium concentrations increased from 1.3 to 9.1 g Na+ L−1. Higher EPS production, particularly a greater predominance of carbohydrates, was stimulated by higher sodium concentrations. This study provides insights into the superiority of sodium tolerance of two-stage anaerobic digester in compared with a single-stage anaerobic system.
Highlights
Anaerobic digestion is often a cost-effective technology for sludge treatment to reduce biosolids and recover energy [1]
This study investigates the effect of sodium on the viability and activity of the methanogens from the second-stage reactor of a two-stage anaerobic system, which could help to provide knowledge for the design, operation and optimisation of the two-stage anaerobic digester for applications on the more saline organic wastes
The total chemical oxygen demand (TCOD) and volatile suspended solids (VSS) were measured in accordance with standard methods [22], and the volatile fatty acids (VFA) measurement was described previously [23]
Summary
Anaerobic digestion is often a cost-effective technology for sludge treatment to reduce biosolids and recover energy [1]. Since the hydrolysis process is the rate-limiting step in the anaerobic digestion of sludge, various pretreatment methods have been proposed to improve the disintegration efficiency of sludge particulates [2]. Alkaline pretreatment with controlled pH is best known for its high efficiency in solubilizing complex substrates [3,4]. The sodium ion would be introduced into the anaerobic system during pH regulation if using sodium hydroxide (NaOH) or sodium carbonate (Na2 CO3 ) [5]. Anaerobic digestion has been reported to be hindered by the presence of high concentrations of sodium ions. The effect of sodium ions on the activities of methanogens
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