2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
- 26 -
Bio-Hydrogen Production from Starch
Wastewater by Dark Fermentation: Effects
of the Cell to Substrate Concentration
Ratio and Initial pH
B. Kanchanakhan
*
, N. Sinbuathong
*
*, S. Leungprasert
*
, and
D. Watts
***
*
Department of Environmental Engineering, Faculty of Engineering, Kasetsart University, (
Thailand
)
*
*
Scientific Equipment and Research Division, Kasetsart University Research and Development Institute
(KURDI), Kasetsart University, (
Thailand
). Correspond to email:
***
Otto H. York Center for Environmental Engineering and Science, New Jersey Institute of Technology, (
USA
)
Abstract
-- This study characterized the effect of the
cell-to-substrate-concentration ratio and the initial pH of
starch wastewater during biological hydrogen production
by dark fermentation. Starch wastewater at 25000 mg
COD/l was processed with heat treated mixed bacteria,
originating from the digested sludge of the plant
generating the starch wastewater, at cell and substrate
concentration ratios of 4 and 0.26 by varying initial
wastewater pH in the range of 4-7. Experiments were
performed in batch processes at 35
0
C. The results showed
effective and fast degradation of starch wastewater when
the system was operated at a Cell:COD ratio of 0.26 g
cell/gCOD and at initial wastewater pH 7. Under these
conditions, the highest yield and specific hydrogen
production rate obtained were 63 ml H
2
at STP/g COD
degraded and 7.38 ml at STP/g cells-hr, respectively.
Index terms
-- Cell Concentration, Hydrogen, pH,
Starch Wastewater
I.
I
NTRODUCTION
Hydrogen (H
2
) production by anaerobic microbial
communities through dark fermentation using organic
waste as the substrate has drawn attention because of its
ability to produce an environmentally friendly energy
source, while simultaneously stabilizing waste. Several
researchers have investigated the possibility of
hydrogen production [1,2,3,4,5] and found that one of
the difficulties associated with hydrogen production
using mixed microbial communities is the coexistence
of hydrogen consuming microorganisms,
such as
methanogens. Several studie
1
s have used heat
treatment of the inoculum selected to seed the reactors
as a method to inactivate or eliminate these undesirable
components of the microorganism mixture. Lay [2] and
Okamoto [6] used wet heat treatment (boiling for 15
This work supported by Kasetsart University Research and
Development Institue(KURDI), Kasetsart University, Bangkok,
Thailand
minutes) of anaerobic digester sludge, whereas Van
Ginkel et al. [7] used dry heat treatment (baking at 104
°C for 2 hours) of compost and soils. The goal for this
heat treatment is to inactivate hydrogen consuming
microorganisms thereby selecting for hydrogen
producing bacteria. There have been many studies
reporting the results of batch experiments using starch
wastewater that found that cumulative hydrogen
formation, H
2
yield, and the specific hydrogen gas
production rate (SHPR) depend on the type of bacteria,
and type of substrate, as well as substrate concentration
[8]. The optimum initial pH of the wastewater for
hydrogen production is different depending on the
parameters above [9,10]. In this study, heat treatment
of the inoculum was employed as a method to increase
hydrogen production by inactivation of non-spore
forming hydrogen-consuming microorganisms leading
to selection for hydrogen producing spore forming
bacteria in batch experiments. The batch experiments
were performed to determine the optimum initial pH for
hydrogen production from starch wastewater by dark
fermentation. Another objective was to find the effects
of the biomass and substrate concentration (Cell:COD)
ratio on hydrogen production. The key performance
indicators utilized are hydrogen yield (ml H
2
produced/gCOD degraded) and the specific H
2
production rate, (SHPR, ml H
2
/ g cell- hr).
II. M
ATERIALS AND METHODS
A. Enrichment Cultures
Digested seed sludge was collected from the bottom
of the upflow anaerobic sludge blanket of a starch
wastewater treatment plant at Chorchaiwat Industry
located in Chonburi province, Thailand. The
concentration of biomass slurry in terms of mixed
liquid volatile suspended solids (MLVSS) was
approximately 20000 mg/l. The mixed bacterial culture
was treated by adding the sludge to test tubes and
