Wetlands are sources of biogas, i.e. methane, which is produced by anaerobic processes that occur during the underwater decomposition of organic material. Methane is produced in a series of fermentation processes where oxygen in absent. Kazda explains that this applies to all wetlands, whether they are in permafrost soils or tropical swamps. The natural processes that happen in anoxic natural conditions are “basically” similar to those that occur in biogas plants, the only differences being dynamics, size, intensity and number of microorganisms present.

“The idea was to transfer the ecological conditions of nature to biogas technology in order to break down organic matter into biogas,” said Kazda describing his bionic approach. In contrast to engineers, biologists like Kazda are more interested in the processes that happen in nature, something that engineers cannot understand in detail. Kazda and his team have four fermenters in the basement of the University of Ulm that they use to investigate how biogenic waste, i.e. food waste, can be efficiently turned into biogas.

Despite some advantages, food waste pulp is difficult to ferment under anaerobic conditions. It has a pH value of 3.5 to 3.8, which makes it rather acidic. Biogas processes only run efficiently at a pH of 7. Fermenters that are fed with quantities of low pH food waste pulp that are too large can quickly impede the production of methane. The bacteria rapidly digest huge amounts of pulp, the formation of acid suppresses all other processes and causes methane production to come to a standstill. The process can be stabilized with additional biofilms. “This works to some extent,” says Kazda but it is definitely not a miracle cure.

In contrast to maize, which is the main renewable used in biogas production, food waste pulp consists of tiny food particles with small surfaces on which only a few microorganisms can grow. Based on investigations carried out in wetlands, Kazda and his team came up with the idea of mixing the biomass contained in the fermenter with chaffed reed mace or wheat straw. This provided the microorganisms with additional surfaces on which they could grow and form biofilms, which in turn rendered the fermentation process more stable. The researchers from Ulm have already successfully implemented their findings into a medium-scale (350 kW) biogas plant run by a farmer from Aulendorf and have been able to considerably increase the production of biogas. 

According to Kazda, the addition of chaffed reed mace and wheat straw has several advantages: in addition to being cheap, the quantity of organic material can be easily adjusted as required. Moreover, the process requires relatively small quantities of reed mace and wheat straw. Kazda: “Finding the optimal mixture that prevents the substrate from becoming too viscous and forming floating layers will involve testing on a case-by-case basis.” Another important aspect is that the plant residues can be spread on agricultural fields in the same way as other fermentation residues.

The project “Increasing the efficiency of biogas production with inoculated plant surfaces” was funded by the “Baden-Württemberg Stiftung” foundation and has now come to an end. However, Kazda and his colleagues from the Department of Microbiology at Ulm University who were involved in the project are already planning and implementing new projects.

Biogas researcher Kazda is continuing his research into substance classes that are difficult to ferment in other ongoing projects. Kazda is investigating the optimal ratio of floating fat mixtures for the effective production of biogas. This involves fats that result from the processing of meat. An exchange project carried out in cooperation with Australian researchers also focuses on the same fats. 

A larger cooperative project with partners from the food industry is already in the concrete planning stage. Huge quantities of organic waste accumulate in the dairy and meat industries; while the majority of these substances are discarded, are other substances used as raw material for other purposes. The use of such waste is subject to complex regulations. “However, only a small proportion of such waste is sensibly used for the production of energy,” said Kazda. Many of the organic substances have a high water content and depositing them in landfills is prohibited in order to minimize their environmental impact. An obvious alternative would be to use them for the production of energy in biogas processes where the generation of methane, whose energy can be converted into electricity and heat, is expressly sought.

In principle, Kazda’s motivation for carrying out biogas research is related to an ecological paradigm, namely ensuring that the substance cycles in nature are kept as closed as possible and also to counteract the depletion of biogenic resources. Kazda believes that such resources are dwindling. He has come up with the following result: there are no biomass reserves that could be used for the production of energy.

There are around 7,100 biogas plants in Germany. Kazda estimates that food waste is only fermented in one out of nine of these plants. This biogenic waste material, which accounts for several million tons per year, along with kitchen waste collected in separate organic waste containers, harbours an energy potential that is not being sufficiently exploited.

Kazda believes that one of the reasons for this is related to the fact that more subsidies are given for using renewable resources than organic waste. Another reason might be that biogas technology is relatively new, and organic waste has only been used for the production of energy in Germany for around ten years. Kazda is therefore not surprised that greater research efforts are devoted to agricultural substrates (renewable resources) than to organic waste. He concludes: “In the same way as nine out of ten biogas plants utilize renewable resources, only one out of ten research projects is focused on the use of waste materials while the nine others are concerned with renewables.”

However, Kazda is convinced that the recycling of waste is starting to gather pace, as the quantities of waste are greater than the quantities of renewables, whose potential is limited. Research interests are not only driven by political conditions. The ecologist from Ulm, who was head of the “Ulmer Initiativkreis nachhaltige Wirtschaftsentwicklung” (Ulm Initiative for Sustainable Economic Development) until 2011, also believes that the producers of biogenic waste are not yet feeling enough pain in their pockets, as disposal costs are currently factored in the product price.

Kazda believes that food producers (e.g. cheese dairies, abattoirs) need to be made aware of the possibility that they can cover their relatively high energy requirements with biogas that can be produced from the waste resulting from the meat/cheese production process. This would considerably increase the degree of self-sufficiency at the same time as reducing the industry’s dependence on energy producers. However, Kazda also emphasises that the food industry has not yet reached this stage, as the production of biogas involves a different technology from that which is typically used by the dairy industry, for example. “I think it is necessary to point the way forward here and show food producers that it is actually possible to use their own waste to produce their own energy,” concluded Kazda. 

Kazda is specifically focused on grasses with a high cellulose content that are difficult to ferment, for example roadside greenery. On the other hand, he is also very interested in compounds that ferment too quickly. Kazda believes that there is still a long way to go before the optimal ratio of substrate mixture is found but he also strongly believes in the future of research into the recycling of biological waste.

Kazda’s major interest, namely nutrient cycles, shows that his ecological approach is not an exotic one. Biogenic waste from the food industry is rich in nitrogen and phosphorus, nutrients that are lost when food waste is dumped in landfills or combusted. The nutrient cycle could be closed if nitrogen and phosphorus were put back on the fields as a valuable fertilizer.

In cooperation with planners, plant manufacturers and a food company, Kazda is involved in a pilot project aimed at generating biogas from food waste and recovering nitrogen and phosphorus through precipitation. He expects the project to become profitable after a period of five years. “Ecology is a science that can be captured in monetary terms,” said Kazda not without a certain degree of satisfaction.