Pumps manufacturer Verder Pumps’ VF25 peristaltic pumps are being used as part of a project by UK-based University of Nottingham Department of Chemical and Environmental Engineering, together with British electrical engineering company Lindhurst Engineering, who have pioneered a new approach to anaerobic digestion (AD), which is based on the development of microbial fuel cell systems through the pumping of cow manure slurry into anaerobic digesters and converting the slurry into commercial volumes of methane gas.

The collaboration resulted in a prototype digester, which has been operating at the university’s Sutton Bonington Campus for almost two years.

The prototype is a modular system that uses a semicontinuous flow process with liquid manure pumped into the process tank where it remains for about 48 hours before being pumped out for disposal.

The Verderflex VF25 peristaltic pumps pump the wet slurry into the digester and then pull it out once it has gone through treatment. The pumps can be reversed to clear the suction lines and run dry without any problems. For this prototype, the pumps were specified to operate at speeds of 12 rpm to 47 rpm and a flow rate of up to 0.8 m3/h and to deliver an operating pressure of 4 bar.

The system is coupled either with a microbial fuel cell or a microbial electrolysis cell, depending on the operating conditions, and made from an array of anodes and cathodes connected to an electrical circuit.

The bacteria naturally present in the slurry tend to grow all around the anode, forming a thick biofilm. The organic substrate is converted into methane, protons and electrons. The electrons flow from the anode through an electrical circuit. The protons migrate from the anode chamber to the cathode chamber, where they recombine with the electrons to form grey water.

Whereas in large AD systems, the required temperature to stimulate the growth of bacteria is typically 37 °C to 40°C, for this process the temperature needed for converting organic compounds into hydrogen and/or methane is much lower, varying between 25 °C and 30 °C.

The additional benefits are a reduction in the chemical content used in the treatment process by 50% in only two days, and the production of biogas with shorter retention times than conventional AD, instead of the typical 20 or 30 days.

Being a semicontinuous flow system, it is reliant on a steady flow of feedstock and this aspect of the process requires a reliable and effective pumping infrastructure.

Following a review of the performance of the original pumps used in the first prototype, two Verderflex hose pumps were introduced. Such was their success that, when it came to further scaling up and building two new units, Lindhurst Engineering turned once again to Verder for its pump requirements.

The Verder VF25 has a proven track record in the biogas processing industry, handling slurries containing mixed solids, as well as those with a low viscosity level. Further factors that will be attractive to operators of the Lindhurst digester, the H2DA, include the pump’s ease of use, low level of maintenance, economic running costs and international availability.

Agricultural Potential
According to Lindhurst Engineering, the design goal of the prototype is to treat slurry waste on a small scale at source much faster than the norm of 20 days. This makes it easier for smaller farm units, owing to the lack of space-consuming storage tanks (which exacerbates capital expenditure costs).

Small-scale farmers can make use of their own slurry, rather than sending it off site for processing, and generate power for the farm itself.

The prototype is a hybrid technology between AD and microbial electrolysis cells, where biogas is produced in the background at higher efficiency and it does not need to have the slurry enriched in order to produce an energy-rich gas.

Currently, the focus is on producing methane, as the quality of the slurry manure that is being treated is more suitable for methane production. However, other than producing heat and power, the technology can produce grey water that can be reused on the farm. It can also produce dry fertiliser that is more advantageous to store and can be spread all year round without limitations.

Verder Pumps
Verder Group includes a large number of wholly owned and joint venture partnership companies that provide a range of products and services.

Verder South Africa, established in 2002, has unlimited access to Verder Group’s international technical and support network, which ensures that the end-user is provided with a omprehensive and value-adding service for the company’s extensive range of centrifugal, industrial hose, peristaltic hose, and air diaphragm pumps.