Bicudo, Jose

Jose Bicudo is a Senior Wastewater Engineer with Associated Engineering with a cross-company role as National Technical Specialist. Jos has 30 years of professional experience in the academic, municipal and consulting sectors. His experience includes facility planning and design, technology demonstration, innovative technologies, biosolids management and resource recovery. Jos is an active member of the WEF Residuals and Biosolids Committee and has served as Chair of the WEAO Residuals and Biosolids Committee for the 2018-2019 term.

Titles from this speaker

Feasibility of Advanced Digestion Options to Reduce Biosolids Volume

Abstract

[Introduction The City of Kelowna Wastewater Treatment Facility (WWTF) is a biological nutrient removal (BNR) plant with capacity to treat approximately 70 MLD of raw wastewater. The facility produces both primary (fermented) solids and secondary (waste activated sludge) solids. The two (2) solid streams are thickened and blended to produce a mixed sludge, which feeds dewatering centrifuges. The undigested dewatered cake is hauled to the Regional Biosolids Composting Facility (RBCF) located near Vernon, BC for composting. The RBCF is jointly owned by the City of Kelowna and the City of Vernon and operated by the City of Kelowna. Undigested solids (including feedstock from Kelowna, Vernon, North Okanagan Regional District, Silver Hawk Utilities), and Lake Country Wastewater Treatment Plants (WWTP) are received at the RBCF and mixed with hog fuel or clean wood chips and composted to produce an organic soil amendment called OgoGrow that meets the BC Organic Matter Recycling Regulation (OMRR) Class A compost criteria. OgoGrow is used by the municipalities and marketed for sale to the public. The total annual processing capacity at the RBCF is capped at 27,000 wet tonnes per year and the City of Kelowna allocation is 18,000 wet tonnes. The current volume of undigested solids production at the WWTF exceeds the City's allocation at the RBCF and solids above 18,000 wet tonnes are sent to an alternative overage facility. As the City's population continues to increase an alternative biosolids management strategy is being considered. Diversion to off-site facilities would be part of a portfolio of biosolids management options. In addition, the City is actively pursuing infrastructure options that will reduce GHG emissions, and biosolids is one important avenue being considered. This paper discusses the feasibility of biosolids management options based on variations and enhancement of anaerobic digestion (AD), which might help address capacity concerns at the RBCF. Different options were analysed for biosolids volume reduction, energy generation and use, life-cycle cost, including sensitivity to select input parameters. A structured decision-making process, using a simplified triple bottom line (TBL) approach, is also included to provide a comparative evaluation of the options and inform the City on a number of important corporate considerations. Anaerobic digestion conceptual design The City defined the objectives of a new digestion facility in a previous study completed in 2020. A preferred AD alternative was identified and proposed to be located on a new site approximately two (2) kilometres away from the current WWTF. Fermented primary sludge (FPS) and thickened waste activate sludge (TWAS) would be pumped from the WWTF through a forcemain. The envisioned new AD Facility would be constructed in phases. In the first phase, the digesters would operate as mesophilic digesters and generate Class B biosolids. With approximately 50% removal of volatile solids through mesophilic digestion, capacity issues at RBCF could be alleviated. In the second phase, the digesters would operate as thermophilic digesters and flow-through vessels would be added for extended thermophilic anaerobic digestion (ETAD). Class A biosolids would be generated due to the thermophilic digestion process, allowing for an additional outlet for the beneficial use of biosolids. The digested biosolids would be dewatered, with cake being hauled to the RBCF for composting or directly to land application, depending on the project phase and operational needs. The initial phase costs were estimated at $78.1M at midpoint of year 2024 construction; the full buildout was estimated to cost $100.4M at midpoint of year 2024 construction. Advanced digestion options Concerns with the estimated high costs of the new Digestion Facility allowed for an additional review of options or variations of the preferred concept that could still generate either Class A or Class B biosolids, promote further reduction in volume (thus freeing up more space at the RBCF), and at the same time generate more biogas to help offset the operational costs of the new Facility. Five (5) options with different digestion configurations that could satisfy the City needs were developed with the 'delayed' ETAD option that was previously developed used as the 'control' option, as follows: -Option 1 - Mesophilic digestion that would generate a Class B biosolids product; -Option 2 - Thermal-hydrolysis process (THP) followed by mesophilic digestion (Full THP) that would generate a Class A biosolids product; -Option 3 - Thermophilic digestion that would also generate a Class A biosolids product; -Option 4 - Delayed ETAD that would initially generate a Class B biosolids product, and later a Class A product (control option); -Option 5 - Mesophilic digestion followed by THP that would generate a Class B biosolids product (but also eventually a Class A product after composting). The two (2) TH options (options 2 and 5) are based on CAMBI's TH technology and configurations. CAMBI has significant TH experience, with a high number of operating facilities in North America and around the world, hence their systems were selected as representative technologies for the purposes of this study. Table 1 provides detailed information on process parameters for each option. Technical comparison A high-level comparison of the five (5) different options will be presented at the full Conference paper, focusing on advantages and disadvantages of each. Financial comparison The five (5) options were compared financially in terms of capital, operation and maintenance (O&M) and life cycle costs. All options were evaluated with and without biogas upgrading to better understand its impact on O&M costs. It was assumed that all biogas produced would be sold to Fortis BC for the biogas upgrading option. Class D (-30% to +50%) cost estimates were prepared for the various options to provide a comparative basis for the evaluation and detailed charts will be included in the full Conference paper. Simplified triple bottom line approach A simplified Triple Bottom Line (TBL) 'plus' approach for structured decision making was used to make a comparative evaluation of the five options. The framework was based on the overarching perspective of 'sustainability' and uses a simplified multi-criteria analysis to integrate technical, environmental, social and economic factors such that a complete picture of the alternatives under evaluation can be provided. Weights were used for each criterium to reflect the City's values and provide a sensitivity analysis of the rankings. The following criteria and factors were selected based on discussions with City staff: -Technical: Biosolids volume reduction and dewaterability, complexity of operation -Environmental: GHG emissions, pathogen regrowth -Social: Odour emissions, Class A versus Class B biosolids -Economic: Life cycle costs GHG emissions and life cycle costs scoring were based on estimates assuming the City would consider two (2) different management strategies: -Generate Biosolids Growing Medium (BGM) from Class A biosolids and Class A Compost from Class B biosolids (emissions shown in Table 2); and -Generate Class A compost from either Class A or Class B biosolids (emissions not shown in this abstract but will be included in the full Conference paper). An initial scoring was conducted using the same weight for the technical, environmental social and economic criteria. Scoring was also conducted using different weights to look at the importance of both economic and non-economic factors and better reflect the City's concerns related to biosolids management. Table 3 shows the scoring and ranking with higher importance given to non-economic factors. Similar scoring tables will be presented in the full Conference paper for increased importance given to economic factors and also to social and environmental factors. Summary and conclusions Based on a simplified TBL 'plus' decision-making analysis, the rankings obtained, and sensitivity analysis conducted, both THP options were found to consistently be the highest scoring or ranking options for each of the management strategies evaluated. Addition of conventional AD as a subsequent step to reduce the volume of biosolids is an appropriate technology for the City to consider. There are a host of issues to consider when contemplating a thermal hydrolysis facility associated with AD. Some municipalities are considering this process as an entirely new facility that would include TH/digestion and related infrastructure. Others are examining options to modify their existing anaerobic digestion process to accommodate TH pre-treatment and to expand or alter the energy producing elements of a facility. Post-digestion THP ranked consistently in first when composting was considered for all Class A and Class B biosolids.

This paper was presented at the WEF/IWA Residuals and Biosolids Conference, May 16-19, 2023.

SpeakerBicudo, Jose

Presentation time

10:45:00

11:15:00

Session time

10:45:00

11:45:00

SessionSession 03: Digestion Optimization and Troubleshooting

Session number03

Session locationCharlotte Convention Center, Charlotte, North Carolina, USA

TopicDigestion & Stabilization