Anaerobic digestion of raw and thermally hydrolyzed wastewater solids under various operational conditions

In this study, high-solids anaerobic digestion of thermally pretreated wastewater solids (THD) was compared with conventional mesophilic anaerobic digestion (MAD). Operational conditions, such as pretreatment temperature (150 to 170 degrees C), solids retention time (15 to 20 days), and digestion temperature (37 to 42 degrees C), were varied for the seven THD systems operated. Volatile solids reduction (VSR) by THD ranged from 56 to 62%, compared with approximately 50% for MAD. Higher VSR contributed to 24 to 59% increased biogas production (m3/kg VSR-d) from THD relative to MAD. The high-solids conditions of the THD feed resulted in high total ammonia-nitrogen (proportional to solids loading) and total alkalinity concentrations in excess of 14 g/L as calcium carbonate (CaCO3). Increased pH in THD reactors caused 5 to 8 times more un-ionized ammonia to be present than in MAD, and this likely led to inhibition of aceticlastic methanogens, resulting in accumulation of residual volatile fatty acids between 2 and 6 g/L as acetic acid. The THD produced biosolids cake that possessed low organic sulfur-based biosolids odor and dewatered to between 33 and 39% total solids. Dual conditioning with cationic polymer and ferric chloride was shown to be an effective strategy for mitigating dissolved organic nitrogen and UV-quenching compounds in the return stream following centrifugal dewatering of THD biosolids.     

The Ythan Project: A Case Study on Improving Catchment Management through Community Involvement

Increased participation in resource management decisions by a wide range of stakeholders has been widely advocated, and has recently been formally incorporated into the European Water Framework Directive. However, achieving such participation has generally proved to be problematical. In response to locally perceived needs, a project was set up in the Ythan catchment in northeast Scotland, to undertake catchment management actions with increased public involvement. This paper outlines the methods used to increase public participation in such actions, and some preliminary assessments of the effectiveness of these. The experience of the project and the lessons learnt, including some of the difficulties of ensuring fully representative stakeholder involvement, are discussed in relation to published criteria for public participation in resource management.