pH dependency of hydrogen fermentation from alkali-pretreated sludge

Abstract

Batch tests were carried out to study the possibility of hydrogen production from alkali-pretreated sludge without seed and the pH dependency of hydrogen fermentation from alkali-pretreated sludge. Experimental results showed that the sewage sludge with alkali-pretreatment could be successfully applied to biologically producing hydrogen without seed and extra-feed. The results also showed that the initial pH value of sewage sludge was an important factor throughout the hydrogen fermentation of alkali-pretreated sludge. The maximum hydrogen yield was obtained at initial pH value of 11.0 (14.4 mL·g VS -1 ). The hydrogen yield of alkali-pretreated sludge at alkaline initial pH value was much higher than that of acidic or neutral initial pH value. The optimal pH value of hydrogen production from alkalipretreated sludge was approximately 9.5. The consumption of hydrogen could be inhibited when the pH value of sludge was above 8.5. The change of hydrogen yield at various initial pH values was similar to that of sludge SCOD. The change of sludge pH value was slow and acetate was the major component of volatile fatty acids produced in the process of hydrogen production. The yield and the constitution of volatile fatty acids were sensitive to the initial pH value.

Effects of various pretreatments on biohydrogen production from sewage sludge

“…The VFA were mainly composed of acetate (45%-76%) and butyrate (12%-22%), being very different from most studies of carbohydrates. The compositions of VFA are similar to the former researches [10][11][12] . The complicated organic components of the four kinds of pretreated sludge, which were degraded in the anaerobic fermentation, were the reason for the different compositions of VFA.…”

“…Many researchers have reported similar results [10][11][12] and methanogenesis is believed to be the main hydrogen consuming action in the anaerobic digestion of sludge [2] . Figure 2 summarizes the changes of methane yields in the anaerobic fermentation of the four pretreated sludge samples.…”

“…The differences of the experimental conditions, such as sewage sludge, initial pH and reactor form, were the reasons causing the differences of the hydrogen yields between this study and the literatures. Figure 1 also shows that the effect of initial pH on the hydrogen yield of four sludge samples was significant because high pH could further disrupt the microbial cell of sludge [10,12] . For example, the hydrogen yield of BS at initial pH of 11.5 was 11.68 mL H 2 /g VS, while that at initial pH of 7.0 was only 1.46 mL H 2 /g VS.…”

“…Ultrasonic pretreatment. The ultrasonic pretreatment was performed with the help of a cell-breaker (SONICATOR-JY92-2D2, Xinzhi Inc., China) at a frequency of 20 kHz [11,12] . The sludge sample (250 mL) was placed in a 300 mL graduated flask with the ultrasonic probe positioned in 3 cm under the surface of sludge.…”

“…Some pretreatment methods, such as thermal pretreatment and alkaline pretreatment, have been used to disrupt the microbial cells and release the organics to liquid so as to enhance the anaerobic digestion of sludge [1,8,9] and biohydrogen production of sludge [10][11][12][13][14] . For example, Cai et al [10] utilized alkaline pretreatment to enhance hydrogen production from sewage sludge.…”