5.2 Natalie Taupe – University of Copenhagen

ReUseWaste > Thesis abstracts > 5.2 Natalie Taupe

Thermal treatment technologies for low moisture and dehydrated manure feedstock, Natalie Taupe, ULIM

Farm and animal wastes are increasingly being explored for gasification and pyrolysis, due to the urgent necessity of finding new waste treatment options. The primary focus of this research was to assess different ways of using low moisture and pre-treated manure feedstock for bioenergy and biochar production and utilization to mitigate environmental burdens.

The first study investigated the use of a farm-scale, auto-thermal gasification system for the production of a heating gas using poultry litter (PL) as a feedstock. Side products were characterised and suggestions given for their practical use. The PL’s ash melting temperature was 639 °C, therefore the reactor temperature was kept around this value. As a result, the process performance parameters were low, with a cold gas efficiency (CGE) of 0.26 and a carbon conversion efficiency (CCE) of 0.44. The calorific value of the clean product gas was 3.39 MJ m-3N (LHV). The tar was collected as an emulsion containing 87 wt.% water and 9.2 wt.%db of nitrogen. An additional consequence of the low reactor temperature was the high amount of remaining char, which was heterogeneous in nature due to the uneven bed temperature.

In the second study the PL gasification char was evaluated for its agronomic value compared to slow pyrolysis chars derived from the same PL feedstock, cow manure (CM) and the solid phase of anaerobically digested pig slurry (PS), all produced at 400 and 600 °C. The char’s chemical and physical properties were compared with the guidelines for European biochar certification. Furthermore, lettuce growth and nutrient uptake of macro- and micro nutrients and the trace element chromium were evaluated. The results show that gasification char did not differ significantly from the pyrolysis chars. CM char has potential to be classified as a biochar, while PL and PS chars are below the minimum carbon content limits (>50 wt.%db). Furthermore, PL and PS chars exceeded the threshold for the heavy metals Zn and Cu (400 g t-1 and 100 g t-1 respectively). With regard to the sewage sludge directive all chars were within the limits. PL and PS chars showed the highest lettuce yield and nutrient uptake, while CM chars did not differ significantly from the control without any fertilizer. Chars produced at 400 °C resulted in a higher nutrient uptake compared to 600 °C chars at short term, however long term experiments are necessary to evaluate the full potential of the manure chars.

In the third experiment a biochar produced in the Kon tiki open fire cone kiln was evaluated to see its effect on reducing NH3 emissions from stored cow slurry. The biochar treated slurry was compared with the untreated slurry, slurry treated with sulphuric acid and mixtures of biochar and sulphuric acid over a six-week period. In addition, CH4 fluxes were monitored. Sulphuric acid decreased NH3 emissions, while biochar had no effect. CH4 emissions were reduced with biochar treated slurry compared to untreated slurry; however, acidified slurry containing biochar increased CH4 emissions due to the added carbon in the slurry mixture. The reduction of CH4 emissions in biochar amended slurries might be attributed to changes in microbial communities. 

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