Conference Agenda

The production of biogas, a renewable resource, was increased using the microbial hydrolysis process (MHP) with anaerobic digestion. Anaerobic digestion performance was enhanced with the MHP using Caldicellulosiruptor bescii (C. bescii), a hyper-thermophilic bacterium. The innovative MHP enhances any anaerobic digestion process by adding a bioaugmentation stage. Digestate from an anaerobic digester (AD) is fed to a hydrolysis tank populated with C. bescii for a hydraulic retention time of 2 days at 75 degrees Celsius (C). The C. bescii hydrolyses cellulose and other recalcitrant volatile solids that are otherwise resistant to digestion into volatile acids. These volatile acids are returned to the AD where methanogens convert them into biogas. MHP was tested at lab-scale and pilot-scale with anaerobic digestion of solids from three water resource recovery facilities (WRRF). The three WRRFs were the City of Gresham Wastewater Treatment Plant in Gresham, OR with mesophilic anaerobic digestion (MAD) and fats, oils, and grease (FOG) addition; Encina Water Pollution Control Facility (WPCF) in Carlsbad, CA with MAD; and Oakland County’s Clinton River WRRF in Pontiac, MI with thermal hydrolysis process (THP) and MAD. These WRRFs had high performing full-scale AD systems averaging 58-60 percent volatile solids reduction (VSR). A test AD system with MHP was compared to a control AD system without MHP. The addition of MHP enhanced the AD performance of all three WRRFs from a VSR of 60 percent to over 75 percent. Enhanced performance would result in a 25 percent increase in biogas production and corresponding reduction in biosolids production. A conceptual design was completed for implementation of MHP at VCS (VandCenter) Denmark’s Ejby Mølle Water Resource Recovery Facility (EMWRRF). A calibrated whole-plant model was used to evaluate MAD performance with and without MHP. The model incorporated VSR results from lab-scale and pilot-scale testing of MHP. Results of modelling at EMWWRF predicted an increase in VSR from 55 to 75 percent corresponding to a 36 percent increase in biogas production.

“Empresa de Acueducto y Alcantarillado de Bogotá (EAAB)”, Bogotá, Colombia, is responsible for the implementation of the Bogotá River Sanitation Program. EAAB currently operates the 90-MGD Salitre WRRF, located on the north end of the city, which is undergoing an upgrade to expand its capacity to 160-MGD. This plant will treat 30% of the city’s wastewater. EAAB recently completed the design of the 370-MGD Canoas WRRF, to be located in the southern end of the city. The Canoas WRRF will treat the remaining 70% of the city’s wastewater, with a total service area population of 7.2 million.

The Canoas WRRF secondary treatment facilities designed include activated sludge step-feed aeration, secondary clarification, and chlorine disinfection. The associated solids train include sludge thickening, sludge pre-dewatering, thermal hydrolysis process (THP), anaerobic digestion (AD), biosolids dewatering, beneficial utilization of biosolids and a Biogas Co-generation facility.

The solids line for the Canoas WRRF was designed with two main objectives: 1) minimize Biosolids production, 2) maximize beneficial utilization and energy recovery.

A critical component of the solids train is the THP/AD system. This process allows less sludge to be generated versus conventional anaerobic digestion, given the greater VSS destruction and improved sludge dewaterability, generating biosolids which can be classified according to its pathogen content as Class A biosolids. This baseline design scenario was later compared with other biosolids minimization processes (thermal drying, solar drying, and incineration, among others), together with a preliminary market study of potential uses of the end product, to determine the most cost-effective solution.

The design also considered biogas utilization for onsite co-generation. The use of Combined Heat and Power (CHP) is anticipated to utilize the biogas for electric energy generation as well as production of the steam required for the THP system. An estimate of 12 MW of electrical power will be generated to cover plant uses (close to 2/3 of the plant’s electrical power requirements). Heat from the exhaust gases of the turbines will be recovered and used to produce the vapor needed for the THP, thus maximizing the energy recovery in the plant, and saving critical electrical energy costs.