Managing an Ever-Changing Stream of Organic Materials for Co-Digestion at the Hermitage Municipal Authority - From Impounded Honey and Rotten Vegetables to Biogas Success

摘要

The Hermitage Municipal Authority ('Authority') completed upgrades at their Water Pollution Control Plant ('WPCP') in May 2014 which expanded wastewater treatment capacity and introduced a Two-Phase Anaerobic Digestion ('2PAD') complex to the current plant operations. This 2PAD complex optimized the solids handling train by further promoting biosolids stabilization, biogas recovery, and the generation of both heat and power. Biogas produced during the breakdown of Volatile Solids in the anaerobic digesters can be collected and be upgraded for several applications including combustion fuels for combined heat and power generation. Although waste activated sludge has been the traditional source of feedstock for the digesters, the Authority has vigorously pursued alternative feedstocks to improve biogas generation and yield. As part of the upgrades completed in May 2014, a liquid based food waste receiving facility was constructed and contains equipment used to puncture, squeeze, and separate liquid food waste from its packaging. The liquid food waste is then collected and conveyed into the 2PAD system for digestion. Deliveries of liquid based food waste to date have largely been liquid or powder and originate from local food manufacturers like Dean Dairy Foods and Joy Cone. Common deliveries included expired milk, yogurt, cottage cheese, cultured butter, half & half, heavy whipping cream, fruit punch, lemonade, iced tea, cake batter, flour, and sugar. While these products have led to increased biogas production through co-digestion and a valuable source of income for the Authority, the Authority felt they were only reaching a portion of the overall market and could expand further their operations with solid based food waste receiving. After completion of pilot testing and market exploration, the Authority constructed in the summer of 2016 a solid based food waste receiving facility and began processing a wider variety of feedstocks for co-digestion. These feedstocks have included vegetable trimmings and cuttings, raw meat, tortillas, black beans, ice cream, whole butter and butter packets, and unseparated food scrapings and trash from institutional cafeterias. With selection and operation of a turbo-separator, the Authority has maintained a high level of feedstock quality and been able to partner with recycling firms for packaging disposal. The Authority's success in handling this wide variety of feedstocks (liquid and solid) has been in part to equipment selection but largely from innovative operations to manage labor requirements with the value of the feedstock in biogas production. These innovations have allowed the Authority to process the food waste with very high organics recovery rates and positioned the Authority to economically compete with traditional food waste disposal methods such as landfilling and composting. These efforts, coupled with marketing of their services, have led the Authority to process food recalls from over twenty-six states and the verified destruction of counterfeit foreign honey seized by the US Treasury Department. This counterfeit honey destruction comprises over 6,000 barrels of honey in a rapid timeframe, with a market value more than 3mm US dollars. This paper will explore the types of feedstocks the Authority has successfully, and in some cases unsuccessfully, processed at the facility and techniques and methods the Authority has pioneered to efficiently handle the wide variety of changing feedstocks. Data will be presented on the increase in biogas production from the various feedstocks and the financial impact, both in tipping fees and in enhanced electrical generation. Biogas formation rates, accelerated by the 2PAD process will also be reviewed to see the impact of thermophilic digestion on the food waste.