Influence Of The PH,Pretreatment And Hydraulic Retention Time On The Enhancement Of The Biohydrogen And Volatile Fatty Acids Production From Food Waste In The Semi-continuously Running Reactor

Food waste(FW)is an untapped source with high potency for resource recovery.Utilization of FW as a substrate in dark fermentation(DF)is a well-studied topic nowadays because FW contains high amounts of organic substance and moisture like lipids,starches,and proteins.DF has the ability to produce from FW high-value byproducts,like lactic acid(LA),hydrogen(H2),alcohols(EtOH),short-chain fatty acids,and methane.Moreover,it has been proved that hydrogen is one of the promising energy sources which is vital for shrinking dependency on fossil fuels.Otherwise,VFAs have a wide-ranging of applications such as the utilization as an alternative carbon source.In this study,FW effluent was used as a substrate for both hydrogen and volatile fatty acids(VFAs)production by a lab scale set up of the semi-continuously running system with a mesophilic fermentation to examine the influence of pretreatment,hydraulic retention time(HRT)and pH(PHP system)on the hydrogen and VFAs production.Additionally,the PHP and uncontrolled system were compared with each other.Primarily,the effect of three different pH(5,6,and 7)and pretreatment(Chemical treatment(CT),Heat treatment(HT),and heat-alkaline treatment(HAT))was investigated.Repeated SAS measurement showed that the factors(pH and Pretreatment)significantly influenced H2 production rate,VFAs concentration VFA/soluble chemical oxygen demand(SCOD),and H2/SCOD traits(P<0.0001).The Duncan comparisons showed that both production rate and yield of H2 were the highest in the chemical treatment(CT)at pH 7,while yield and concentration of the VFAs were the highest in the chemical treatment(CT)at pH 6 having VFAs concentration(55.44±2.39)g/L,VFAs yield(926.21±42.27)mg/g SCOD along with the H2 yield(4.44±0.10)ml/g SCOD,and H2 production rate(280.82±5.72)ml/L.While the difference between pH 7 and pH 6 for the VFAs production was not high.The butyrate and acetate for the optimal blend(pH 6,CT pretreatment)counted for 62.43%of the total VFAs.On the other hand,the results showed that pH 5 is not beneficial for H2 and VFAs production.Furthermore,a trial was established to study the effect of HRT where three different HRT(HRT1:2d,HRT2:3d,and HRT3:4d)were applied to evaluate their impact on H2 and VFAs production at pH 7 and CT treatment.One way-ANOVA showed that the factor HRT has a highly significant impact on the H2(production rate and yield)where the highest production was at HRT2,accounted for(263.82±18.44)ml/L and(5.19±0.40)ml/g,respectively.On the contrary,HRT has no significant impact on the VFAs concentration but significant influence on the VFAs yield having the highest VFAs yield(823.55±58.38 mg/g SCOD)at HRT3 while the changing in HRT from 2d to 3d led to change in the VFAs concentration from 36.03±1.72 to 40.19±1.53 g/L.The butyrate was dominant,which accounted for 50%of the total VFAs.Also,the results showed that HRT1 has the lowest H2 and VFAs production.The hydrogen and VFAs producers were detected at all HRT levels by denaturing gradient gel electrophoresis(DGGE)of the polymerase chain reaction(PCR)-amplified V3-V4 regions of 16S rDNA analysis.The results showed that the high diversity of the microorganisms was at HRT2,which has the highest hydrogen(production rate and yield),and VFAs concentration.The predominant genus was among all samples;it was proved that Lactobacillus does not affect hydrogen production.The existence of the Clostridium-butyric is the reason of the butyrate acids fermentation in this study.The clostridia are essential bacteria for hydrogen production in the study.Moreover,the comparison between the controlled system PHP and the uncontrolled system at the same HRT levels was studied.Paired-Samples t-test showed that the PHP system has a highly significant difference with the uncontrolled system(P<0.0001)for the H2 and VFAs production.Where H2 production rate was 0.19 ml/L at the uncontrolled system while was 263.82 ml/L at PHP system.On the other hand,PHP was 1.8 times higher than the uncontrolled system for VFAs production.Due to the success of the PHP system in rising the H2 and VFAs production from FW,it would be the ideal solution.