Kraakman, Bart

Bart Kraakman is an Associate Director of Process Engineers at Jacobs.

Titles from this speaker

Description: Odors and Air Pollutants 2023 cover

Deep Sewerage Tunnel Ventilation & Odor Control Design and Operational Experiences in Hot Climate Conditions

Abstract

Several countries in the Middle East have experienced accelerated growth since the mid-1970's when their current sewerage systems were designed. The Abu Dhabi Sewerage Services Company (ADSSC) is the service provider for sewerage services throughout the Emirate of Abu Dhabi. Many of its existing sewerage infrastructure assets were overloaded and reaching the end of their intended life. ADSSC embarked on a major capital improvement program (CIP). One of the key components of the CIP was the construction of a deep tunnel which includes approximately 40 kilometers (km), 25 miles of deep tunnel sewer (with internal diameters of 4.0, 5.0 and 5.5 meters; which equal 13, 16 and 18 feet, respectively), as well as over 50 km (30 miles) of micro-tunnelled link sewers, a large new main tunnel pumping station at the downstream end of the deep tunnel sewer (largest PS in the world) and the decommissioning of 35 existing sewerage pumping stations. One of the key challenges faced by the implementation of the deep tunnel was related to tunnel ventilation and odor control. With the proposed tunnel route passing through some of the premier developed areas, the directive from higher authorities was clear; no odors and limited odor control facilities would be permitted. To accomplish the stated goal, a unique approach of several (regional) odor control systems were designed and installed along the new deep tunnel and at the downstream tunnel pumping station. Proper sizing, appropriate treatment technology, careful siting, and effective operation were required to ensure the deep tunnel, drop structures, and link sewers were well ventilated and maintained at a negative pressure under all normal operating conditions and that emissions were controlled to prevent offsite odor impacts. By so doing, odors would be contained and removed, helping assure ADSSC's goal of no odors would be achieved. Each regional odor control system consists of multiple extraction fans, first stage biotowers, a treated effluent water feed system, and final stage carbon polishing units. The regional odor control systems were designed to extract air directly out of the tunnel, retaining the concept of allowing drop structures to naturally ventilate link sewers and allowing the regional systems to extract the air collected within the tunnel for treatment. Given the size and complexity of this massive investment, the project design team elected to proceed with a physical model study during the design stage. The model study aimed to validate and refine certain design concepts associated with the drop shaft structures with an emphasis on hydraulic performance and the proposed odor control approach. In addition, CFD modelling of vortices and sewer hydraulics was performed to optimize the design. Moreover, liquid and headspace sampling of the sewer network was undertaken during the design stage as well as during the first years of operation when the Deep Tunnel Sewer was slowly taken online. A detailed analysis study was conducted a few years after initial start-up and commissioning for the purpose of quantifying performance and identifying areas of improvement. To address the challenges associated with analyzing the complexities associated with the existing tunnel and link sewers, a sewer process computer model was completed for simulating the various operating conditions and gaining understanding of possible root causes for some odor generation and fugitive emissions. The results of all measurements and the modelling were documented and analyzed, and some key findings from the study included: The main odor hotspots were identified:

Inadequate ventilation from the deep tunnel due to operational issues at the regional systems

Highly septic sewage entering the deep tunnel at several locations

Surcharging of local network pipe in some areas

Best fit solutions for each odor hotspot provided

This presentation will share some key lessons learned from (a) the design methodology during the detail design phase, (b) the commissioning during start-up phase, and (c) the first few years of operation.

This paper was presented at the WEF Odors and Air Pollutants Conference, May 16-19, 2023.

SpeakerKraakman, Bart

Presentation time

10:45:00

11:15:00

Session time

8:30:00

11:15:00

SessionPlant & Interceptor Vapor Phase Planning Controls Odors/Corrosion

Session number11

Session locationCharlotte Convention Center, Charlotte, North Carolina, USA

TopicCollection System Odor Control

Author(s)

B. Kraakman

Author(s)B. Kraakman 1; S. Cowden 1

Author affiliation(s)Jacobs1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2023

DOI10.2175/193864718825158758

Volume / Issue

Content sourceOdors and Air Pollutants

Word count16

Full-scale Digester Micro-Aeration Studies to Improve Biogas Quality

Abstract

ABSTRACT
Biogas generated from anaerobic digestion typically requires gas conditioning before it is used to generate energy. Elevated concentrations of hydrogen sulfide (H2S) in the biogas is often a limitation for downstream processing of biogas. Full-scale tests using micro-aeration technology was undertaken at several water resource recovery facilities and showed that this new process-integrated technology has potential using minimum plant upgrading while contributing to the sustainability and economic efficiency of the energy recovery process of waste sludge digestion at water resource recovery facilities (WRRFs). Keywords: anaerobic digestion, biogas, energy recovery, hydrogen sulfide, micro-aeration.

BACKGROUND
Biogas generated from anaerobic digestion of sludge typically requires gas conditioning before it is used to generate energy. The high concentration of H2S in biogas typically entails a limitation for downstream processing of the biogas as it creates maintenance related corrosion problems in combustion engines, and the release of SOx in ‚ue gases. Traditional physical/chemical end-of-the-pipe technologies (i.e. chemical scrubbing using caustic/hypochlorite or iron oxide-based adsorbents) are relatively expensive and can present relatively high environmental impacts. Biotechnologies (i.e. aerobic or anoxic biotrickling filtration) or physical-chemical combinations with biotechnology (i.e. caustic scrubbing followed by biological oxidation) have recently emerged as cost-effective and more environmentally friendly alternatives. Nevertheless, these biotechnologies are still limited by their high investment costs and their generated byproducts such as sulfuric acid and/or elemental sulfur slurry that need further processing or disposal. Micro-aeration, which involves the dosing of a small amount of air during the digestion process, is a process-integrated biochemical method of removing H2S from the biogas. Micro-aeration has been researched and used in industrial biogas plants, but rarely tested at municipal WRRFs. It has been applied in eastern-Europe in full-scale sludge digesters at WRRFs, with H2S removal efficiency of more than 90% in most cases. Moreover, micro-aeration improved the degradability of COD and volatile suspended solids in all cases. The studies discussed in this presentation are, as far as the authors know, the first full-scale tests in Spain and North-America that try to overcome the lack of full-scale experience with micro-aeration in digesters at WRRFs.

OBJECTIVE
The main objective of this presentation is to share information about micro-aeration and explain how it has potential as an effective digester biogas conditioning technology. The presentation will include research and full-scale testing data and information. These full-scale experiences may provide a stepping-stone for further development and wider implementation.

METHODOLOGY
Micro-aeration technology was tested over a period of several months in different full-scale digesters at different WRRFs. A small amount of air was injected in the sludge recirculation mixing pipe after the pump using fine bubble air injection nozzles or in the headspace of the digesters. The biogas H2S concentrations and sludge characteristics such as pH, alkalinity, total solids, volatile solids were measured daily, while the biogas production and sludge feed were measured continuously.

RESULTS
A comparison between the different types of digesters (i.e. digesters with mechanical mixing and digesters with internal biogas recirculation for mixing) are made to provide better understanding in how micro-aeration can best be applied. An example of the reduction of the H2S concentration in the biogas before and after introducing the micro-aeration process is illustrated in Figure 1. The H2S concentration in the produced biogas dropped by more than 80% from 5,000 ppmv to less than 1,000 ppmv when the micro-aeration was stopped. Directly after stopping the micro-aeration the H2S concentration increased back up to 5,000 ppmv. Figure 1: Reduction of H2S in the biogas during the initial phase 1 of one of micro-aeration tests. The presence of small amounts of oxygen in the anaerobic digestion process in the full-scale test did not significantly impact neither on organic matter removal nor on the biomethane productivity when the amount of air injected is limited. In fact, these full-scale tests (like other bench-scale studies) revealed that, besides efficiently desulfurizing biogas, micro-aeration can potentially improve organic matter degradation during municipal sludge digestion. The volatile solids content dropped in this full-scale test by a few percent from about 66.6% without to about 63.6% with the micro-aeration technology. This drop in volatile solids and a potential more stable digestion process was likely caused by the higher hydrolysis rates and/or alleviation of sulfide toxicity. The potential capital cost savings as well as operational cost savings that micro-aeration technology can provide is substantial. The cost saving on iron sponge media change-out are determined and will be presented. Some of the lessons learned from the full-scale tests include (1) the effectiveness of the air injection method using fine bubble air injection nozzles, (2) the identification of the locations where not to install the nozzles and (3) the quantification of the consequence of overdosing of the injected air amount. Multiple full-scale application of MA in digesters have been reported for different type of digesters (Table 1). The overview shows the different full-scale applications including digester size, organic feed material, biogas production, digester mixing method, biogas production and H2S reduction obtained in the biogas. In general, 80 to over 95% of H2S reduction have been achieved in multiple full-scale applications. Table 1: Example of Full-scale Digester Micro-Aeration Studies and Applications for Biogas Desulfurization.

CONCLUSION
From the full-scale tests and related research, it can be concluded that micro-aeration technology holds great potential for being an effective gas conditioning technology for different types of digesters along with requiring minimal capital investment and operating costs. Micro-aeration would also further contribute to the sustainability and economic efficiency of the energy recovery process during the waste sludge digestion at a WRRF.

The following conference paper was presented at Odors and Air Pollutants 2021: A Virtual Event, April 20-22, 2021.

SpeakerKraakman, Bart

Presentation time

09:00:00

16:00:00

Session time

09:00:00

16:00:00

SessionInnovation

Session number5

Session locationOn Demand

TopicAnaerobic Digestion, Biogas Cleaning, Micro-Aeration

Author(s)

Bart KraakmanIsrael DiazJosef CescaMunoz Raul

Author(s)Bart Kraakman1; Israel Diaz2; Josef Cesca3; Munoz Raul4;

Author affiliation(s)JACOBS1; University of Valladolid2; CH2M/ Jacobs3; University of Valladolid4

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Apr 2021

DOI10.2175/193864718825157922

Volume / Issue

Content sourceOdors and Air Pollutants Conference

Word count9

Micro-Aerobic Digestion For Advanced Process Stability and Biogas Desulfurization

Abstract

INTRODUCTION Many anaerobic digestors have not been fully driven to its stable performance potential. Despite the many merits, the anaerobic digestion (AD) process has several drawbacks such as low hydrolysis rates, unstable at high organic loading rate, and release of toxic/corrosive hydrogen sulï¬de (H2S). Suboptimal AD performance may mean under-utilised biogas production, foaming events, or poorly dewatered cake. Traditional AD processes will benefit from a facelift that maximizes biogas production, enhancing process stability and broadening substrate treatability without major infrastructure modification. Moreover, elevated concentrations of H2S in the biogas is often a limitation for downstream processing of biogas that typically requires expensive gas conditioning before it is used to generate energy. This facelift could be given by implementing micro-aeration, a process-integrated technology that is defined as a system with zero concentration of oxygen present in the sludge and limited (trace) consumption of oxygen. Bench-scale and full-scale tests of organic waste digestion processes using micro-aeration technology was undertaken. The tests confirmed that this process-integrated technology has potential to use minimum plant upgrading while contributing to the sustainability and economic efficiency of the energy recovery process as operated for example at water resource recovery facilities (WRRFs). Pre-treatment processes such as THP is installed progressively to improve the bioavailability of the organic substrate in the digester and bust the methane production. Despite the advantages of a high-thermal pre-treatment processes, microbes in the feedstock have been killed-off resulting in a different, and potentially a reduced diverse microbial community in the digesters, which could make the AD process vulnerable. Biogas generated from anaerobic digestion of sludge typically requires gas conditioning before it is used to generate energy as it can create maintenance related corrosion problems in combustion engines, and the release of SOx in ï¬‚ue gases. Micro-aeration has been researched and used in industrial biogas plants with H2S removal efï¬ciency of more than 90% in most cases (Jenicek et al., 2017, Diaz et al., 2017, Kraakman et al., 2019). Moreover, micro-aeration has shown to improve the degradability of COD and volatile suspended solids in some cases and enrich the diversity of the microbial community potentially improving process stability. OBJECTIVE The main objective of this presentation is to share information about micro-aeration and explain how it has potential to enhance the digestion process and improve the biogas quality. The presentation will include bench-scale research and full-scale testing data as well as several lessons learned. METHODOLOGY Three main full-scale case studies at different WRRFs are used to illustrate the potential and the challenges when implementing micro-aeration technology. For these case studies micro-aeration was tested over a period of several months and up to one year. In all cases, air was injected in the sludge recirculation pipeline after the recirculation pump using fine bubble air injection nozzles. The biogas H2S concentrations and sludge characteristics such as pH, alkalinity, total solids, volatile solids were measured daily using industry standard methods, while the biogas production and sludge feed were measured continuously. Separately, bench-scale testing focused on investigating benefits from micro-aeration on digestion stability and performance. 20-L bench-scale digestion testing used Napier grass (5 months old, a typical energy crop) with and without micro-aeration with cattle manure-derived inoculum were performed at OLR of 5.0â€¯g VS/L/day. Microbial community structure and function were investigated by the analysis of 16S rRNA gene and meta-genomics sequencing. RESULTS Bench-scale research at an organic loading rate of 5 g volatile solids (VS)/L/day showed increased digester stability and performance with micro-aeration, operating at residual acetic acid concentrations of 3.0 g/L, compared to instable control at 9.2 g/L without aeration introduction as shown in Figure 1 (Nguyen et all., 2019). The test digester with micro-aeration also showed an increase in methane yield. 16S rRNA gene sequencing analysis shows increase in relative abundance of facultative bacteria with micro-aeration, while the dominance of hydrogenotrophic methanogens remained similar with and without micro-aeration (Wu et all., 2021). Full-scale micro-aeration test were performed mainly as a means to reduce H2S concentration in the biogas. An example of the reduction of the H2S concentration in the biogas before and after introducing the micro-aeration process is that the H2S concentration in the produced biogas dropped by more than 80% from 5,000 ppmv to less than 1,000 ppmv in the first case study; the second case study showed a decreased H2S concentrations from 1,000 ppmv to 200 ppmv (see Figure 2). The presence of small amounts of oxygen in the anaerobic digestion process in the full-scale test did not impact the biomethane productivity when the amount of air injected is limited. In fact, these full-scale tests (like other bench-scale studies) revealed that, besides efficiently desulfurizing biogas, micro-aeration can potentially improve organic matter degradation during municipal sludge digestion. However, not all attempts of implementing microaeration have resulted in consistent H2S removal; the third case study showed that the overall average was only 40% suspected to be due to limitations in oxygen transfer. The potential capital cost savings as well as operational cost savings that micro-aeration technology can provide is substantial (see Table 1). Lessons learned to be shared as part of this manuscript and presentation are related to: - method and locations for micro-air injection - full-scale implementation design including safety measures - potential risk of elemental sulfur accumulation in downstream equipment - process model development to support process understanding and optimization CONCLUSION From the full-scale tests and related bench-scale research, it can be concluded that micro-aeration technology holds great potential for being an effective gas conditioning technology and enhance the digestion process, while requiring minimal capital investment and operating costs. Micro-aeration would further contribute to the sustainability and economic efficiency of the energy recovery process of organic waste digestion as operated for example at WRRFs.

Many traditional anaerobic digesters can benefit from a facelift that maximizes biogas production and enhancing process stability without major infrastructure modification. Moreover, a simple method to limit H2S in the biogas would all contribute to the sustainability and economic efficiency of the energy recovery process as operated at many water resource recovery facilities. Micro-aerobic digestion can provide this facelift without major infrastructure modification.

SpeakerKraakman, Bart

Presentation time

14:00:00

14:15:00

Session time

13:30:00

15:00:00

TopicIntermediate Level, Biosolids and Residuals, Energy Production, Conservation, and Management, Research and Innovation

Author(s)

Kraakman, Bart

Author(s)Bart Kraakman1; Adrian Romero1; Israel Diaz2; Zhuoying Wu3; Matt Noessen1; Raul Munoz2; Samir K. Khanal4; Po-Heng Lee3

Author affiliation(s)JACOBS, Bristol, UK / Charlotte, USA/ Seattle, USA1; Institute of Sustainable Processes, University of Valladolid, Spain2; Dept. of Civil & Environmental Engineering, Imperial College London, UK3; Department of Molecular Biosciences and Bioengineering, University of Hawaii, Honolulu, USA4

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2022

DOI10.2175/193864718825158628

Volume / Issue

Content sourceWEFTEC

Word count10