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Digestate produced during anaerobic digestion of food waste is recognised as a good alternative to mineral fertilizer which could also be used to amend soil properties. This has conventionally been applied directly and unprocessed to nearby farms or processed and transported elsewhere. The latter option has gained recognition due to environmental restrictions coupled with soil nutrient management objectives but is an expensive venture. With increasing biogas production and AD plants across Europe, production of digestate has however exceeded its demand. Improving the dewaterability of the digestate has the benefit of reducing the cost and time of processing and handling. The principal aim of this experiment was to enhance the dewaterability of food waste digestate by the addition of pulp fibre to the AD process. In doing so, the study also investigated the effect of co-digestion of food waste and pulp fibre on the performance and stability of the digestion. Source separated food waste was digested at OLR of 3.5 ±0.1 g VS/L*d-1 for 163 days in 3 CSTRs with a working volume of 6L at HRT OF 23-26 days. Soft- and hardwood pulp fibres were added to 2 designated digesters for 104 days and increased stepwise at OLR of 0.5 ±0.1 g VS/L*d-1 PF until 1.5 ±0.1 g VS/L*d-1 PF with the 3rd digester serving as a control. 3 other post-digesters, each with a working volume of 1.41L were operated for 104 days with sludge from the 3 main digesters serving as inoculum and substrate. This was run at HRT of 7 days.  Pulp fibre addition of 1.5 ±0.1 g VS/L*d-1 OLR to 3.5 ±0.1 g VS/L*d-1 food waste increased the total biogas and methane production to 35-40% and 21-32% respectively. Though recording a higher biogas production, the corresponding specific methane production from the fibre addition was 12-8% lower than food waste digestion. Analysis of the digestate from post digestion showed that CST increased linearly from 595 ±13s for food waste digestate to 962 ±19s for pulp fibre addition. The experiment established a positive correlation between CST and organic matter content. Suspended solids increased from 128 ±10 mg/l for FW digestate to 177 ±12 – 237 ±10 mg/l for fibre addition. Addition of kraft pulp fibre types did not enhance the dewaterability of the digestate. However, the total methane production was enhanced by the addition of pulp fibre. / <p>Parts of the thesis is scheduled to be published in a scientific journal</p>

Sustainable agriculture is a crucial factor to be considered in order to meet the growing demand for food production. The need for low cost and highly functional materials to provide the most efficient cultivation process has led the agriculture industry to consume petrochemical and mineral based material in an enormous amount. Thus, disposal of the used mulch materials has become a serious environmental issue. In this work, the possibility of using wood pulp fibre in two distinct applications in agriculture is investigated. First, agricultural mulching is the subject of the study and second, we focus on using wood pulp fibre as growing medium in greenhouses. Mulching in agriculture is an essential practice in order to have high crop yield, healthy products, and more efficient cultivation process. Over the years, agricultural mulch has been made out of a variety of materials. The most common of all is plastic mulch due to its low price and high functionality. However, the problems associated with applying and removing the enormous load of plastic and their disposal have made it an option far from ideal. Therefore, there is a need to develop mulches based on biodegradable materials. Paper-based mulch is one of the candidates, In the first chapter of this work, with a review of previous works in this area, we attempt to develop a new spray-able mulch based on wood pulp fibre. A novel foam forming method is utilised to deposit wood pulp fibres in combination with other chemicals as an evenly distributed fibre network on a porous bed. Currently available paper based-mulch is of a very high basis weight. In first part of this work, application of a foam formed low basis weight paper-based mulch is investigated. Whereas, in the second chapter, the use of wood pulp fibres in a similar function as “rockwool” in soilless greenhouse farming is investigated. Rockwool is named after fibres made of melted minerals at temperatures as high as 2000°C. Rockwool is used as blocks for seeds growth and propagation and as an alternative for soil in greenhouses. The feasibility of microenvironment control of the rockwool blocks in crop production plus its low cost have made is popular. However, their disposal has always been an environmental issue. The biodegradability of wood pulp fibres is a great advantage over mineral fibres used in rockwool. In the second chapter of current work, we study the possibility of using wood pulp fibres as carriers for agriculturally beneficial chemicals. Specifically, we focus on binding and release properties of small organic molecules from wood pulp fibres. The goal is to achieve an understanding of the capability of wood pulp fibres to be used in building biodegradable growing medium blocks in greenhouses. / Thesis / Master of Applied Science (MASc)