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Abstract

This study investigated the effect of five different pre-treatment methods (ammonia (NH3), caustic soda (NaOH), dry milling, hot water and steam explosion) for straw for biogas production. The methods were selected based on their suitability for implementation in farm-scale biogas plants. The pre-treatment methods were applied to four different types of straw. Batch anaerobic digestion tests were carried out in bottles at mesophilic temperature (37 ± 1 °C). The straw was analysed for lignin, hemicellulose and cellulose. The results showed large variations in methane production following the different pre-treatment methods. There were also large variations between the pre-treatment methods in their effect on the different types of straw. Pre-treatment with NaOH on barley straw was particularly effective. The results also showed that the shorter the retention time in the reactor, the more important the choice of pre-treatment method. Different pre-treatment methods were found to be optimal, to some extent, for different retention times.

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Abstract

The awareness of sediment and nutrient loss from non-point sources are of increasing environmental concern as measures to reduce point source inputs to surface waters have been introduced. Mitigation efforts to reduce loss of particles and nutrients from agriculture in Norway and other countries have mainly focused on surface runoff, whereas sub-surface drainage has received little attention. However, research has shown that the sub-surface field drains are transporting both sediment and nutrients rapidly to the watercourses. Despite these established facts there has been little development of measures to reduce these losses. This article describes how Lightweight Aggregates (LWA), Leca®, can mitigate some of the environmental challenges connected to sub-surface field drains. A field experimental project was performed to assess the effects on drainage water quality hydrological performance and functionality of drainage systems based on Lightweight Aggregates compared to traditional pipe drains. Registrations of the performance of the systems were done in two separate periods, 1992–1993 and 1999–2000. After 2000 no measurement programme has run. The functionality of the drainage systems was registered in connection to ordinary farming activity. In 1999–2000 LWA drains showed particularly good performance with regard to reducing the content of Phosphorus, 40–90 % reduction in Total-P. The drainage water from the LWA drains contained less than half the amount of suspended solids compared to traditional pipe drains. The results from 1993 showed no significant difference between LWA drains and pipe drains with respect to Nitrogen. The results from 1999/2000 showed higher loss of Nitrogen through pipe drains with no envelope compared to all other systems. LWA drains may be particularly useful in reducing particles and nutrient loads from cultivated flat drained areas adjacent to environmentally sensitive and ecologically important water ecosystems. Further investigations are recommended to optimise the design of LWA drains.