Microbial and Chemical Processes in Natural and Engineered Systems

In the last few years, the environmental engineering and science community has lost several of our preeminent leaders and pioneers, and this special issue honors them: Edward (Ed) Bouwer (1955–2019), Michael (Mike) Aitken (1956–2020), James (Jim) J. Morgan (1932–2020), Deborah (Deb) Swackhamer (1954–2021), and Philip (Phil) Singer (1942–2020). All five were accomplished researchers, as well as dedicated mentors, teachers, advisors, and colleagues. All were pioneers, establishing new paths of research scholarship, conducting groundbreaking scientific discovery, advancing technologies for pollution control, writing definitive textbooks, supporting the profession through service on Boards and committees, and leading national policy discussions on water quality and environmental pollution. Building a sense of community was very important to each of these pioneers. Their home departments and schools, along with future generations of engineers and scientists, will continue to benefit from their efforts through the strong bonds that each of these leaders built with their students, alumni, and colleagues, both throughout academia and in the professional world.

Building on the contributions of these five giants in our field, this special issue of Environmental Engineering Science presents high-quality, high-impact papers that focus on the innovative microbial and chemical processes for addressing both classic problems (e.g., nutrient recovery and wastewater treatment) as well as emerging problems (e.g., biodiversity loss, plastic pollution, biotransformation of organic chemicals, cyanotoxins, and disinfection by-products). The manuscripts are grouped by subdisciplinary area and the leaders they honor.

The first eight papers focus on microbial processes and honor the legacies of both Ed Bouwer and Michael Aitken. Mike Aitken exemplified leadership both at his home institution and across the environmental engineering community. He was a Fellow of AEESP and was the President in 2002. He is best known for inspiring the changes that led to the biennial AEESP conferences. Ed Bouwer was internationally recognized for his research on drinking water and wastewater treatment, microbial processes for the treatment of legacy and emerging contaminants, and fate and transport of contaminants. His PhD dissertation research with Perry McCarty on the biological transformation of chlorinated solvents and his continued study of this topic throughout his career were instrumental to the development of in situ bioremediation processes. He studied many different applications of using microbial processes including the treatment of pharmaceuticals and personal care products; the application of biofiltration for drinking water treatment; and the anaerobic treatment of algal biomass for methane production. His breadth of contributions has inspired the newest AEESP Outstanding Doctoral Dissertation Award.

Ed Bouwer and Mike Aitken, both experts in microbial processes, were dedicated to ensuring their work had a direct and positive impact on the world. Similarly, the authors of the first two papers report on methods to enhance the sustainability of the processes studied. Amer and Kim (2023) present innovative methods for the rapid and selective enrichment of Cupriavidus necator in mixed cultures to achieve more cost-effective production of polyhydroxyalkanoate on an industrial scale. Linvill et al. (2023) conducted an energy balance on full-scale anaerobic wastewater treatment facilities, demonstrating that anaerobic membrane bioreactors and partial nitritation/anammox can achieve an energy positive condition.

Building on Ed Bouwer's work on the biotransformation of organic chemicals, Bealessio et al. (2023) reported on the alcohol-dependent cometabolic degradation of several chlorinated aliphatic hydrocarbons and 1,4-dioxane by Rhodococcus rhodochrous strain ATCC 21198, demonstrating their potential for in situ bioremediation. Ramos-García and Freedman (2023) also investigated cometabolism, in this case, that of 1,4-dioxane under aerobic conditions by the mixed propanotrophic culture ENV487. They demonstrated the potential for using aerobic cometabolism to treat groundwater contaminated with 1,4-dioxane. Ibrahim et al. (2023) demonstrated that activated carbon as an adsorptive biofilm surface (biological granular activated carbon) was much more effective and resilient for the treatment of synthetic produced water under hypersaline conditions as compared to aerobic granular sludge and conventional activated sludge systems.

Motivated by a concern for the effects of polycyclic aromatic hydrocarbons (PAHs) on public health, Mike devoted his career to studying the biodegradation of PAHs in both the soil and aqueous environments. Similarly, out of a concern for public health and the impact on ecosystems, Hunter and Ramsburg (2023) studied the biotransformation of atenolol, a pharmaceutically active compound. Atenolol was believed to be degraded by denitrifying mixed culture communities via endogenous cometabolism or metabolism by a specialized fraction. Gough et al. (2023) investigated the microbial community structure in family-scale rural anaerobic digesters in Nepal. They reported that observed differences in the microbial communities suggest that, among the studied digesters, there are different substrate conversion pathways and a major role of Archaea beyond methanogenesis. The injection of emulsified vegetable oil (EVO) into permeable reactive barriers has been proposed for the remediation of nitrate plumes. To advance this technology, Gonsalez et al. (2023) developed and evaluated a process-based modeling approach for simulating denitrification by EVO, allowing for determination of carbon dosing, longevity, and effectiveness in denitrifying permeable reactive barriers.

Papers 9 and 10 honor Jim Morgan, whose research on aquatic chemistry provides the foundation for the treatment of metals in wastewater and drinking water. The textbook, Aquatic Chemistry, which he coauthored with the late Werner Stumm, remains the standard reference on the subject and has been cited >25,000 times. Quiambao et al. (2023) studied the co-occurrence of microplastics and metals in field sites. In laboratory studies, they found that microplastics served as a substrate surface for the adsorption and nucleation of uranium precipitates. Their findings demonstrate the importance of understanding the occurrence and interfacial interactions of microplastics and metals in the aquatic environment. Chromium contamination of groundwater is a significant environmental problem, especially for marginalized communities dependent on groundwater for drinking and irrigation. Singh et al. (2023) developed a rapid and affordable measurement tool for assessing chromium contamination and a treatment process using ferrous sulfate and slow sand filtration.

Deb Swackhamer is honored through Papers 11 and 12 for her accomplishments in the field of environmental organic chemistry. Deb recognized the urgency of keeping our waters safe and uncontaminated. She championed care for the environment and was unafraid to show others how to accomplish this. In her later career, she served with distinction as Chair of the U.S. Environmental Protection Agency's Scientific Advisory Board. She was also a role model, being one of the first women chemists in the environmental field. In line with her work, the study of Grokowsky and Borgerding (2023) focuses on environmental organic contamination; in their case, due to perfluorinated alkyl substances (PFAS). They describe a nontargeted approach for the detection and identification of PFAS using low-resolution triple quadrupole mass spectrometry, thus making PFAS analysis accessible to more laboratories. Despite the ubiquitous nature of microplastics in the environment, there are no standard methods for sample collection, processing, and the analysis/detection of microplastics. Kosuth et al. (2023) examined three common practices involved in microplastic processing, enumeration, and particle characterization. Their findings underscore the importance of quality control measures for determining microplastic concentrations in the environment.

The last four papers honor the legacy of Phil Singer, who was an internationally renowned expert in water chemistry, chemical oxidation processes, and drinking water treatment. He, along with Jim Morgan, was a member of the National Academy of Engineering, and Phil served as a member of the AEESP Board of Directors. His research primarily focused on minimizing human exposure to substances called disinfection by-products (DBPs), which are created when the chemicals used to disinfect water react with naturally occurring organic material or anthropogenic chemicals. DBPs can cause cancer, and Singer was devoted to lowering DBP concentrations to keep communities safe. Noe et al. (2023) reported that pre-oxidation with ozone, free chlorine, or both limited the formation of N-nitrosodimethylamine (NDMA), a disinfection by-product formed in waters treated with chloramines as a disinfectant. Gawankar and Masten (2023) reported on a rapid screening method using methylene blue dye to assess the reaction kinetics and identify the radicals produced during oxidation by persulfate, which was added in the form of monopersulfate, and peroxide in the presence of ferrous ions. The method was then employed to study the degradation of microcystin-LR by persulfate in the presence of humic acid and bicarbonate. Harmful algal blooms (HABs) are increasingly affecting the quality of source waters for drinking water systems, resulting in the need for new technologies to remove the associated cyanotoxins. Elliott and MacKay (2023) found that neither sodium hypochlorite nor potassium permanganate pre-oxidation treatment resulted in increased susceptibility of cyanobacteria cells to mechanical shear and, thus, did not result in the release of cyanotoxins. This study will help utilities manage their response to HABs in their source waters. Huang et al. (2023) demonstrated that phosphate-based corrosion inhibitors may lead to a rapid depletion of residual disinfectant during stagnation in the presence of phosphate-based biofilms. The depletion of residual disinfectant could have a significant impact on public health, especially in aged and compromised distribution systems.

For more information about the five leaders who inspired this special issue, follow these links to the memorials provided by their home institutions. Ed Bouwer https://hub.jhu.edu/2019/10/09/ed-bouwer-environmental-engineering-obituary/. Michael Aitken https://sph.unc.edu/sph-news/unc-gillings-community-mourns-professor-emeritus-mike-aitken/. Phil Singer https://sph.unc.edu/sph-news/research-never-ends-dr-philip-singer-renowned-water-expert-has-died/. Deb Swackhamer https://www.hhh.umn.edu/news/remembering-deborah-swackhamer-researcher-and-environmental-advocate. Jim Morgan https://www.caltech.edu/about/news/james-jim-j-morgan-19322020