The role of biomass and biorefineries in a sustainable future

Some o f the biggest issues facing humanity in the 21st century include energy security, global warming and resource scarcity. These issues will affect every nation and Ireland is no exception. There is much research underway to uncover technologies that will allow the world to overcome such problems, but none offer the flexibility o f biomass. Unlike other sustainable technologies, which offer a solution to one or at most two o f the above problems, biomass as demonstrated by the author, can play a part in mitigating all o f the above problems. It has been known for some time that biomass can be used in various ways as a form o f renewable energy, but with the development o f biorefineries biomass can be used to produce material as well as fuel products. In this report the author has looked at the viability and benefits o f biomass, bioenergy and biorefining in Ireland. The author has demonstrated that such technologies when implemented correctly are sustainable from an economic, environmental and societal point o f view. The author has shown in this thesis that abundant supplies o f biomass make bio re fineries a viable business opportunity in Ireland and has shown how a number o f biorefinery scenarios have the potential to be extremely profitable. The author has evaluated the profitability o f material product-based bio re fineries as well as fuel productbased configurations. The author demonstrated that value-added co-products help to make bio refineries profitable even when excise-relief is not granted on bio fuels. In this thesis the author has revealed some o f the problems that bioenergy and biorefineries have had to overcome to date and examines challenges that remain for bioenergy and biorefining, and looks at the future opportunities for bio fuels. This report concludes that biomass and biorefining has exciting business potential while offering unique opportunities to mitigate the problems o f the future.

The appraisal of anaerobic digestion in Ireland to develop improved designs and operational practice

Mesophilic Anaerobic Digestion treating sewage sludge was investigated at five full-scale sewage treatment plants in Ireland. The anaerobic digestion plants are compared and evaluated in terms of design, equipment, operation, monitoring and management. All digesters are cylindrical, gas mixed and heated Continuously Stirred Tank Reactors (CSTR), varying in size from 130m3 to 800m3. Heat exchanger systems heat all digesters. Three plants reported difficulties with the heating systems ranging from blockages to insufficient insulation and design. Exchangers were modified and replaced within one year of operation at two plants. All but one plant had Combined Heat and Power (CHP) systems installed. Parameter monitoring is a problem at all plants mainly due to a lack of staff and knowledge. The plant operators consider pH and temperature the most important parameters to be measured in terms of successful monitoring of an anaerobic digester. The short time taken and the ease at which pH and temperature can be measured may favour these parameters. Three laboratory scale pilot anaerobic digesters were operated using a variety of feeds over at 144-day period. Two of the pilots were unmixed and the third was mechanically mixed. As expected the unmixed reactors removed more COD by retention of solids in the digesters but also produced greater quantities of biogas than the mixed digester, especially when low solids feed such as whey was used. The mixed digester broke down more solids due to the superior contact between the substrate and the biomass. All three reactors showed good performance results for whey and sewage solids. Scum formation occurred giving operational problems for mixed and unmixed reactors when cattle slurry was used as the main feed source. The pilot test was also used to investigate which parameters were the best indicators of process instability. These trials clearly indicated that total Volatile Fatty Acid (VFA) concentrations was the best parameter to show signs of early process imbalance, while methane composition in the biogas was good to indicate possible nutrient deficiencies in the feed and oxygen shocks. pH was found to be a good process parameter only if the wastewater being treated produced low bicarbonate alkalinities during treatment.