How to write a paper on fermentation engineering

Biogas fermentation method and fermentation system for supplying energy to greenhouse

Abstract: A patented biogas fermentation method and fermentation system capable of supplying energy to a greenhouse are described. The fermentation system specifically consists of a bioacidification and fertilizer accumulation device, a buffer adjustment tank, a high-efficiency biogas generating device, an effluent sedimentation tank, an effluent storage tank and a biogas caching device, which are sequentially connected by pipelines and valves. The specific steps of the fermentation method include the start-up of the bioacidification fertilizer accumulation unit and bioacidification storage of raw materials, the start-up of the high-efficiency biogas generator unit, biogas production and supply, shutdown and restart. This technology has certain advantages over traditional biogas technology in that it is capable of timely feeding the plantation organic waste generated throughout the year scattered according to the actual greenhouse production into the acid-producing fertilizer pond, and then producing biogas through the fermentation system at any time according to the greenhouse energy supply demand. The fermentation residue is taken out in batches for greenhouse organic fertilizer according to production needs. This technology realizes the requirement that biogas fermentation can be flexibly adjusted according to the greenhouse demand.

Keywords: biogas; greenhouse; energy supply; adjustability

1. Introduction

The greenhouse is an important technological theme in modern agricultural engineering, and the development of greenhouses has transformed the traditional open-air agriculture into controllable agriculture under protected conditions [1]. Currently, greenhouses are widely used internationally for flower and vegetable cultivation [2]. The biggest advantage of greenhouse cultivation is to obtain the maximum production benefits by controlling the greenhouse environment to meet the optimal living conditions of crops and resist natural disasters and so on. In greenhouse management, greenhouse winter heating, supplemental light and carbon dioxide fertilization are important environmental regulation measures [3]. These regulation processes require energy consumption, which is currently dominated by primary fossil energy coal and secondary energy diesel and electricity [4]. The large consumption of these energy sources on the one hand increases the burden of energy supply for the whole society, and on the other hand, it also substantially increases the production costs of products. Affected by energy prices, many greenhouses have to give up the greenhouse winter heating, supplemental light and carbon dioxide fertilization, which not only fails to give full play to the proper function of the greenhouse, but even results in the failure of greenhouse management.

In greenhouse management, a large amount of organic waste from the planting industry is produced every year. Currently, these wastes, which are stacked haphazardly, cause serious agricultural surface pollution [3, 4]. However, these organic wastes themselves are rich in a large amount of organic matter, which is a very good raw material for biogas production. If biogas can be produced from organic wastes generated during greenhouse production and management, thus replacing non-renewable energy sources such as coal, oil, and electricity for greenhouse energy supply, it can not only reduce the cost of greenhouse energy supply, but also the nutrients in the wastes can be recycled to reduce waste emissions and improve the agricultural environment. However, there is no successful case of biogas application in the field of greenhouse energy supply so far.

2. Deviation of traditional biogas technology from greenhouse energy supply demand

Biogas fermentation technology can be divided into two categories, namely, traditional biogas fermentation technology and water-soluble organic matter efficient biogas fermentation technology [5, 6]. Both types of technology applied to greenhouse biogas supply have many technical difficulties. Specifically analyzed as follows:

Traditional biogas fermentation technology, the use of complex organic matter fermentation of biogas, biogas production has a very large cyclical, often the beginning of the feed gas production slow, the middle of the gas production, and once the biogas fermentation system started, whether or not to produce biogas and how much biogas to produce, subject to the characteristics of the raw material and the inherent constraints of the law of fermentation, it is difficult to regulate. While greenhouse energy use is manifested in heating, carbon dioxide fertilization, etc., these energy demands are often controlled by the weather, which is unpredictable. Therefore, there is often no gas when you want gas, do not want gas when the gas production, if you want to meet the demand will have to establish a huge gas storage device, which is not permitted in terms of investment and land occupation. If according to long-term weather forecast for planned feeding, in theory feasible, but in practice is difficult to operate. On the one hand, long-term weather forecasts are currently less accurate, and on the other hand, it is impossible to accurately predict gas production patterns regarding complex organic matter. At the same time, greenhouses produce organic waste that is dispersed throughout the year, and most of the waste produced is perishable and difficult to store. Therefore, the traditional biogas technology is basically unable to adapt to the greenhouse energy supply needs.

High-efficiency biogas fermentation technology for water-soluble organic matter, which utilizes soluble and simple microorganisms for biogas fermentation, can achieve high efficiency by adopting high-efficiency reactors [7,8]. One is that the soluble organic matter is very easy to react, and the amount of biogas produced is within the range allowed by the reactor load, which is basically determined by the amount of feed in the short term, i.e., more feed produces more gas, less feed produces less gas, and stopping the feed for a short period of time means that the gas production stops. Secondly, the anaerobic microorganisms of biogas fermentation in the mature reactor have very strong starvation resistance, and the microorganisms in the reactor can tolerate it for a long time without feeding for a long period of time, and they can quickly return to the normal and efficient gas production when restarted. The above two technical characteristics of efficient biogas fermentation of water-soluble organic matter meet the requirement of fluctuation of greenhouse energy demand. However, if water-soluble organic matter is deliberately purchased as the raw material for fermentation to produce biogas for greenhouse energy supply, not only the cost is not competitive with fossil energy, but also the purpose of local utilization of biomass waste resources, circular economy and environmental construction cannot be achieved. Therefore, the efficient biogas fermentation technology of water-soluble organic matter is also not suitable for greenhouse energy supply needs.

3. Technical content

This paper provides a biogas fermentation system and a fermentation method that can provide a usable biogas fermentation system and a fermentation method for greenhouses according to the actual greenhouse production, and then produce biogas at any time through the fermentation system according to the greenhouse energy supply demand. Among them, the fermentation system consists of a bio-acidifying fertilizer accumulation device, a buffer regulating tank, a high-efficiency biogas generating device, an effluent settling tank, an effluent staging tank, and a biogas caching device sequentially connected by pipelines and valves. The structure is shown in Figure 1. Among them, the bio-acidification fertilizer device and buffer pool set the main control valve, buffer pool and high-efficiency biogas generator set between the pump, high-efficiency biogas generator, water sedimentation tank out of the water storage pool through the gravity of water to complete the connection between the pool, the water out of the storage pool at the same time with the buffer regulator and bio-acidification fertilizer device connected to the middle of the pump and the water distributor in order to set the pump, high-efficiency biogas generator is connected to the methane gas caching device.

In order to ensure that the biogas fermentation can meet the greenhouse energy demand, the above fermentation system is managed according to the following steps

Firstly, the start-up of bio-acidification fertilizer accumulator and bio-acidification storage of raw materials are carried out as follows

(1) Collecting greenhouse planting organic waste or other planting organic waste as start-up raw materials in accordance with a quality equivalent to 2.5-3.5 times of the greenhouse's average daily generation volume, and collecting the greenhouse planting organic waste or other planting organic waste as start-up raw materials. Organic waste as starter raw materials, crushing pre-treatment of starter raw materials;

(2) adding N-containing elemental substances to the pre-treated raw materials obtained in step (1), mixing, and controlling the carbon to nitrogen ratio of the mixture to be (20:1) to (30:1);

(3) inputting the mixed materials obtained in step (2) into the first-use bioacidification fertilizer accumulation device, adding inoculum for Inoculation, mixing, to get fermentation raw materials, the amount of inoculum added to the start of the dry weight of raw materials 3% to 5%;

(4) to step (3) in the bio-acidification of fertilizer accumulation device to add water for fermentation, the amount of water added to at least higher than the start of the raw material plane 10cm, the fermentation temperature is controlled in the range of 20 to 40 ℃;

(5) after 4 to 5 days of fermentation, the fermentation solution pH value fell to 6 or less, that is, the start of the acidified fertilizer accumulation device is completed;

(6) in accordance with the method of steps (1) to (2) at any time to collect and treat the organic waste from greenhouse production, timely input into the bio-acidified fertilizer accumulation device has been activated, without inoculation, directly add water to the raw material plane above the 10cm;

(7) repeat the steps (6) until a bio-acidified fertilizer accumulation device is full, the Re-activate another bio-acidified fertilizer device, repeat steps (1) to (6);

Second, the start of high-efficiency biogas generator, regulating the device to meet the greenhouse energy use and biogas production coordination, the specific methods are as follows:

(1) high-efficiency biogas generator to start: put inoculum into the high-efficiency biogas generator, with water or water with bio-acidified fertilizer device pumped acid mixture. The acid mixture pumped out from the device is filled with biogas generator and left to stand still for 3~5d, and the amount of inoculum added is 3~10kgVSS/m3; the organic acid solution pumped out from the bio-acidification fertilizer accumulation device is pumped into the buffer regulating pool, and regulated by the system effluent or foreign water in the effluent staging pool, and the concentration of chemical oxygen demand (COD) of the organic acid solution is controlled to be 2,000~5,000mg/L as the biogas fermentation Adjust the hydraulic load in stages according to the rate of 0.5kg COD/( m3-d) to 2kg COD/( m3-d), and feed the material continuously until the hydraulic load of 5kg COD/( m3-d) to 10kg COD/( m3-d) is realized, that is to say, complete the startup of biogas generator, and the whole startup will take about 50 to 80 d. During the startup period, the temperature is controlled to be 25 to 35℃. During the start-up period, the temperature is controlled at 25~35℃. The principle of load adjustment is that each hydraulic load adjustment runs stably before starting the next stage of load increase; the effluent of the biogas generating device will flow into the effluent temporary storage pool after settling in the sedimentation tank, partly as the liquid replenishment of bio-acidification and fertilizer accumulation device, and partly used in the buffer regulating pool for the fermentation material adjustment of the acid

(2) Biogas production and supply: the biogas demand will be budgeted based on the greenhouse production actuality. (2) Biogas production and supply: according to the time and quantity of the actual budget biogas demand for greenhouse production, according to 1kg COD production 0.4 ~ 0.5m3 biogas equivalent to the number of demand for organic acid liquid and time, and on time and in accordance with the amount from the bio-acidification of fertilizer accumulation device pumping acid into the buffer regulator pool, according to the method described in step (1) to regulate into the biogas fermentation material; according to the flow rate of 5kg COD ( m3-d) ~ 30kg COD ( m3-d) hydraulic load, the intermittent or continuous way to the already started good acid fermentation material regulating the use of the buffer regulator pool. The biogas is fed into the activated biogas generator for biogas production in a continuous manner, and the produced biogas goes to the biogas caching device for backup; the flow rate control of the feed, intermittent or continuous manner depends on the biogas demand and the volume of the biogas caching device each time. When the biogas demand is large and the volume of the biogas caching device is small, a large flow rate is used for continuous feeding, and vice versa, a small flow rate is used for intermittent feeding; when the extract from a bioacidifying fertilizer accumulator is less than 800 to 1000 mg/L, that is to say, the bioacidifying fertilizer accumulator stops producing acid and stops continuing to extract fermentation liquid from the device.

(3) Biogas production shutdown: For a good start-up and the greenhouse does not need to use biogas, or a biogas use cycle is over and the greenhouse does not use biogas for a long time, stop feeding into the high-efficiency biogas generator and the device enters into shutdown state. During the rest period, the fermentation feed is replenished every 10-30d to ensure the nutritional needs of the microorganisms in the system. The adjustment method of replenishment of fermentation material is the same as that described in step (1); the amount of replenishment of fermentation material is 1-3 times of the volume of the reactor, and the replenishment rate is 2-5kg COD/(m3-d).

(4) Re-starting of biogas production after suspension: for the high-efficiency biogas plant which has been suspended in step (3), it must be re-started before entering into a new gas cycle; the method of re-starting is to adjust the fermentation material in accordance with the method described in step (1) for 3-10d before the start of the new gas cycle, and to adjust the fermentation material according to the method described in step (1), and to adjust the fermentation material according to the method described in step (1), with the amount of the fermentation material being 1.8kg COD/(m3-d) to 2.2 kg COD/(m3-d). (m3-d) load to the high-efficiency biogas plant for adaptive feeding.