| This paper was supported by National"863"high-tech research projects "Research on small and medium-sized bio-hydrogen systems by photosynthetic bacteria with solar energy and its working characteristics" (NO. 2006AA05Z119) and National Natural Science Foundation"Research on thermo effect of bio-hydrogen systems by photosynthetic bacteria (PSB)and the mechanism of hydrogen production by PSB" (NO. 50676029).With the growing depletion of fossil fuel and environmental pollution caused by fossil fuel, people recognized it is necessary to search for clean renewable energy resources to meet the demands of economic development and social progress. Hydrogen is considered as a clean and efficient energy carrier because it has high energy density, produces only water after combustion and can be used as different forms, (such as combustion directly, fuel cell). It is dreamed to develop "hydrogen economy" and "hydrogen society" under widespread use of hydrogen as main energy source in the future.At present, hydrogen production mainly comes from fossil fuels, which is a high energy consumption process and easily causes environmental pollution. It is inevitable that the depletion of fossil fuel will put it to an end. However, bio-hydrogen production is considered to be the main approach to get hydrogen in the future because as a process of microbial metabolism it can be run in normal temperature and has rich source of raw materials. Among the various technologies for bio-hydrogen production, hydrogen production by PSB becomes a focus due to the use of the organic waste as substrates and high conversion yields, which serves as energy supply and waste treatment.PSB can convert organic matter into molecule hydrogen under anaerobic condition with light. The development of photobioreactor is the key link putting hydrogen production by PSB into market from lab research. What's more, with the growing market demand, the development of continuous photobioreactor is the basic condition for the industrialization of hydrogen production by PSB.The design idea to develop continuous large-scale photobioreactor by PSB was put forward in the paper based on the survey of literatures. A continuous photo-bioreactor of hydrogen production by PSB was designed successfully, which use sunlight as the main light source and LED as the auxiliary light source.Main research results of the paper are as following:(1) Built-in illumination and multi-point light sources distribution in reactor are applied. Built-in illumination can overcome the limitation of reactor materials and light supply, which makes it easier to have heat preservation for the reactor and provide a large room as much as possible. Multi-point light sources distribution model guarantees all space in the reactor to get enough light. Meanwhile, it is an effective way to decrease the running cost using sunlight as a main light source and artificial cold light source as auxiliary light source.(2) The long-range transfer of sunlight to the internal reactor would be achieved by the illuminating optical fiber, by which harmful radiation to PSB in sunlight would be filtered. Compared with other types of optical fiber, the multi-core plastic polymer optical fiber has many advantages, and it could not only transmit light in complex path, but also help to realize the multi-point light distribution in reactor. It is essential to choose artificial cold light source to make up the shortcomings of solar energy resulting from its cyclical and instability to keep continuous working. From the result of experiment, light-emitting yellow LED (Light-Emitting Diode) was chosen as the auxiliary light because it is better than other treatments for the growth and hydrogen production of PSB.(3) Although the initial gas components in headspace of reactor would affect the growth and hydrogen production of PSB in a certain extent, a small amount of air in headspace of reactor has no significant inhabitation for hydrogen production. Thus, replacement of the air in reactor with inert gas can be ignored in the continuous photo-bioreactor design, which demands the volume of headspace should be less than 1/3 of the reactor volume.(4) A continuous photo-bioreactor of hydrogen production by PSB was developed, which includes the reactor, the solar heat collectors and heat exchanger unit, sunlight focus and transmission unit, solar photovoltaic unit, gas collection and storage unit and automatic control unit.The baffled structural of the photobioreactor can arrange the illumination in different space of the reactor, as well as realize reactant mixed and stirred during its flow. The design volume of reactor is 5.76 m3; and the working volume is 5.18 m3. 228 glass tubes were arranged in proportional spacing in reactor, which were used to keep the optical fiber and LED out of liquid. Solar vacuum tube collector, 6m2, was used to provide heat for the reactor, and the volume of heat water tank is 1.3 m3. Stainless steel finned tube heat exchanger was used in the reactor, the diameter of tube isφ20mm, and the exchange area is 8.6 m2. The surface of sunlight focus equipment is 2.7 m2. In order to provide electricity for 2days need, solar cell capacity was designed for 120Wp and battery capacity for 180Ah.(5) Research showed that rapeseed oil was better than other defoamers, which did not suppress the growth and hydrogen production of PSB, and had a strong anti-foaming capacity. The economy adding amount of rapeseed oil was 0.05 %, which would form a thin layer on the surface in the reactor.(6)The start experiment of the photobioreactor showed it was necessary to add nutrients such as (NH4)2SO4,NaCL,KH2PO4 and only if a supplement more than 30% of inoculums could keep the photo-bioreactor producing hydrogen steadily when only using glucose as a single substrate for hydrogen production.(7) The effect of glucose concentration on hydrogen yields and stable operation of the reactor was significant. Under the same experimental condition, the hydrogen yield increased with the increase of glucose concentration, the highest hydrogen yield was got at 3% glucose. But the phenomenon changed when the glucose concentration was more than 4%, since the rapid degradation of high concentration glucose would lead to acidification of the solution in the reactor, which is harmful to PSB and decreases the activity of Nitrogenase. However, the average content of hydrogen in the production gas was kept in the same levels with different substrate concentration, but it had changed in different apartment in the same concentration.(8) Different HRT tests showed that the short HRT could reduce the inhibition to the following reaction, but too short of HRT will decrease the utilization of raw materials, even cause incomplete degradation. Although extending the HRT is better for improving the utilization, the longer residence of byproduct will decline the hydrogen production rate. In the test, the maximum hydrogen production rate is 4.225m3/m3·d when the HRT was kept at 36h.(9) Different livestock and poultry dejecta were tested as substrates in hydrogen production; the result showed the cattle dejecta with pretreatment is suitable for producing hydrogen than pig dejecta and chicken dejecta. Cattle dejecta treated for 5~ 7days under dark and anaerobic condition can achieve the optimal results. In the test, the maximum production rate of hydrogen was 0.56 m3/m3·d at 7000mg/L COD with treated cattle dejecta. The production of hydrogen reduced when the solution at a lower concentration due to shortage of the material which can be used by PSB as substrate, but too much higher concentration will effect light penetration and prevent PSB from absorbing enough light energy to meet the demand of electron transport process.
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