Impact of alkali and heat pretreatment on the pathway of hydrogen production from sewage sludge

Abstract

Due to the presence of various types of hydrogen-producing bacteria and numerous organics such as protein and carbohydrate, sewage sludge is a potential material for biological hydrogen production. In this study, two batch tests were carried out to investigate the impact of alkali and heat pretreatment on the pathway of hydrogen production from sewage sludge. The results showed that the heat treatment had a stronger lethal effect on bacteria than the alkali treatment, and could effectively kill hydrogen-consuming bacteria. The heat treatment was more suitable for enriching acidophilic hydrogen-producing bacteria, while the alkali treatment was more suitable for enriching basophilic hydrogen-producing bacteria. A maximum hydrogen production of 10.32 mL/g-COD from alkali pretreated sludge was obtained at an initial pH of 11; while a maximum hydrogen production of 8.94 mL/g-COD from heat pretreated sludge was obtained at an initial pH of 5. Hydrogen production in alkali conditions (pH>9) from alkali pretreated sludge mainly depended on the fermentation of protein by protein-utilizing bacteria; whereas hydrogen production in acidic conditions (pH<6) from heat pretreated sludge mainly depended on the fermentation of carbohydrate by glucose-utilizing bacteria. sewage sludge, alkali pretreatment, heat pretreatment, hydrogen production Citation:Wei S Z, Xiao B Y, Liu J X. Impact of alkali and heat pretreatment on the pathway of hydrogen production from sewage sludge.

Evaluation of biohydrogen production from glucose and protein at neutral initial pH

“…Many studies have reported similar results about biohydrogen production of glucose, other carbohydrates and carbohydrate e contained wastes [2]. Although the result of protein was similar with the study conducted by Bai [18] and Akutsu et al [19] in which peptone was also used as the hydrogen-producing substrate, it was not inconsistent with the studies of our previous studies [6,9] and Guo et al [5], in which sludge (a protein-contained waste) was used. The cumulative hydrogen production showed similar increases as the substrate increased, and the cumulative hydrogen production was much higher when glucose was used as the substrate than when protein was used.…”

“…While it seemed the short fermentation time (only 58 h) in the test could not completely change the microbial species of sludge but change the dominant microorganisms of sludge. Comparing the results of this study with the studies at alkaline pH for protein and ones at acid pH for glucose [9,27,28], it could be found that the DGGE band numbers of this study were far more than the previous studies, which suggested that these microorganisms in the anaerobic fermentation of this study were more abundant than these previous studies. The abundant microorganisms may be due to the anaerobic fermentation at initial pH was favorable the growth of microorganisms.…”

“…For example, Cai et al [6] found hydrogen consumption existed at low initial pH (4e10.5) and not at high initial pH (>11.0) in the biohydrogen fermentation of alkaline pre-treated sludge. While in our previous study [9] few hydrogen consumption was observed in the anaerobic fermentation of the alkaline pre-treated sludge supernatant (which contained 2.14 g protein/l) at high initial pH value (>9.0).…”

“…Although the previous studies found that the pH is an important influence factors of biohydrogen production and the optimal pH of biohydrogen production from carbohydrate is acidic pH (about 4.5e6.0) [1,2] and that from protein is alkaline pH (about 8.5e10) [6,9], the traditional treatment of these organic wastes by anaerobic fermentation usually carries out at neutral pH condition, in which biohydrogen production is only a middle process. Additionally, the initial pH of these wastes and wastewater usually is neutral pH and controlling pH at acidic pH or alkaline pH will increase the cost of anaerobic fermentation and the requirement of reactor on acid-resistant and alkaline-resistant.…”

A state-of-the-art review of biohydrogen producing from sewage sludge

“…Alkaline pretreatment can hydrolyze protein and nucleic acid, damage the enzymes and structures of cells, decompose saccharides, and attack cell walls, releasing intracellular polymers and supplying substrate for sludge fermentation. Wei et al revealed that sludge pretreated with alkali was more suitable for the enrichment of basophilic hydrogen‐producing bacteria. In addition, hydrogen production mainly relied on the fermentation of protein by protein‐utilizing bacteria if sludge was pretreated at alkaline conditions.…”