Trace and bulk organics removal during ozone-biofiltration treatment for potable reuse applications

Removal of organic micropollutants in biologically active filters: A systematic quantitative review of key influencing factors

Biofiltration utilizes natural mechanisms including biodegradation and biotransformation along with other physical processes for the removal of organic micropollutants (OMPs) such as pharmaceuticals, personal care products, pesticides and industrial compounds found in (waste)water. In this systematic review, a total of 120 biofiltration studies from 25 countries were analyzed, considering various biofilter configurations, source water types, biofilter media and scales of operation. The study also provides a bibliometric analysis to identify the emerging research trends in the field. The results show that granular activated carbon (GAC) either alone or in combination with another biofiltration media can remove a broad range of OMPs efficiently. The impact of pre-oxidation on biofilter performance was investigated, revealing that pre-oxidation significantly improved OMP removal and reduced the empty bed contact time (EBCT) needed to achieve a consistently high OMP. Biofiltration with pre-oxidation had median removals ranging between 65% and >90% for various OMPs at 10-45 min EBCT with data variability drastically reducing beyond 20 min EBCT. Biofiltration without pre-oxidation had lower median removals with greater variability. The results demonstrate that pre-oxidation greatly enhances the removal of adsorptive and poorly biodegradable OMPs, while its impact on other OMPs varies. Only 19% of studies we reviewed included toxicity testing of treated effluent, and even fewer measured transformation products. Several studies have previously reported an increase in effluent toxicity because of oxidation, although it was successfully abated by subsequent biofiltration in most cases. Therefore, the efficacy of biofiltration treatment should be assessed by integrating toxicity testing into the assessment of overall removal.

Contaminants of emerging concern reduction and microbial community characterization across a three-barrier advanced water treatment system

This research investigated the removal of contaminants of emerging concern (CECs) and characterized the microbial community across an advanced water treatment (AWT) train consisting of Coagulation/Flocculation/Clarification/Granular Media Filtration (CFCGMF), Ozone-Biological Activated Carbon Filtration (O3/BAC), Granular Activated Carbon filtration, Ultraviolet Disinfection, and Cartridge Filtration (GAC/UV/CF). The AWT train successfully met the goals of CECs and bulk organics removal. The microbial community at each treatment step of the AWT train was characterized using 16S rRNA sequencing on the Illumina MiSeq platform generated from DNA extracted from liquid and solid (treatment media) samples taken along the treatment train. Differences in the microbial community structure were observed. The dominant operational taxonomic units (OTU) decreased along the treatment train, but the treatment steps did impact the microbial community composition downstream of each unit process. These results provide insights into microbial ecology in advanced water treatment systems, which are influenced and shaped by each treatment step, the microbial community interactions, and their potential metabolic contribution to CECs degradation.

Pathogen reduction by ozone-biological activated carbon-based advanced water reclamation for reuse

Ozone-biological activated carbon (ozone-BAC)-based technologies are emerging as an appealing option for potable reuse systems; however, uncertainty remains regarding the reduction of waterborne pathogens. Common log reduction requirements have been modeled after California Department of Drinking Water's 12-10-10 log reduction value (LRV) for enteric virus, Cryptosporidium, and Giardia, respectively. The objective of this research was to investigate appropriate LRVs of pathogens that can be achieved in ozone-BAC-based treatment systems and to assess the applicability of employing drinking water pathogen guidelines for potable reuse applications. A pilot scale ozone-BAC-based treatment train was operated at two water reclamation facilities in Reno, Nevada, USA. Virus, Cryptosporidium, Giardia, and bacterial indicators were monitored across individual and combined treatment processes. Pathogen barriers investigated include conventional filtration, ozonation, and ultraviolet disinfection. Based on sampling and treatment validation strategies, the three pathogen barriers can provide minimum LRVs of 13-9-9.5 for virus, Giardia, and Cryptosporidium. Secondary biological treatment can provide additional pathogen LRVs with site-specific sampling. The present study addresses regulatory uncertainties associated with ozone-BAC pathogen reduction. PRACTITIONER POINTS: Ozone-biological activated carbon-based advanced treatment can meet pathogen LRV requirements with a minimum of three pathogen barriers. Successfully applied drinking water pathogen reduction guidelines for potable reuse applications verified by operational criteria. Low presence of pathogens requires surrogates and indicator analyses and variety of monitoring techniques to verify pathogen log reduction.

Demonstration-scale evaluation of ozone-biofiltration-granular activated carbon advanced water treatment for managed aquifer recharge

The Sustainable Water Initiative for Tomorrow (SWIFT) program is the effort of the Hampton Roads Sanitation District to implement indirect potable reuse to recharge the depleted Potomac Aquifer. This initiative is being demonstrated at the 1-MGD SWIFT Research Center with a treatment train including coagulation/flocculation/sedimentation (floc/sed), ozonation, biofiltration (BAF), granular activated carbon (GAC) adsorption, and UV disinfection, followed by managed aquifer recharge. Bulk total organic carbon (TOC) removal occurred via multiple treatment barriers including, floc/sed (26% removal), ozone/BAF (30% removal), and adsorption by GAC. BAF acclimation was observed during the first months of plant operation which coincided with the establishment of biological nitrification and dissolved metal removal. Bromate formation during ozonation was efficiently controlled below 10 µg/L using preformed monochloramine and preoxidation with free chlorine. N-nitrosodimethylamine (NDMA) was formed at an average concentration of 53 ng/L post-ozonation and was removed >70% by the BAFs after several months of operation. Contaminants of emerging concern were removed by multiple treatment barriers including oxidation, biological degradation, and adsorption. The breakthrough of these contaminants and bulk TOC will likely determine the replacement interval of GAC. The ozone/BAC/GAC treatment process was shown to meet all defined treatment goals for managed aquifer recharge. PRACTITIONER POINTS: Floc/sed, biofiltration, and GAC adsorption provide important barriers in carbon-based treatment trains for bulk TOC and trace organic contaminant removal. Biofilter acclimation was observed during the first three months of operation in each operating period as evidenced by the establishment of nitrification. Bromate was effectively controlled during ozonation of a high bromide water with monochloramine doses of 3-5 mg/L. NDMA was formed at an average concentration of 53 ng/L by ozonation and complete removal was achieved by BAFs after several months of biological acclimation. An average 25% removal of 1,4-dioxane was achieved via oxidation by hydroxyl radicals during ozonation.

Microbial community in biofilters for water reuse applications: A critical review

The combination of ozonation (O₃) and biofiltration processes has become practical and desirable in advanced water reclamation for water reuse applications. However, the role of microbial community and its characteristics (source, abundance, composition, viability, structure) on treatment performance has not received the same attention in water reclamation biofilters as in other applications, such as in drinking water biofilters. Microbial community characterization of biofilters used in water reuse applications will add evidence to better understand the potential microorganisms, consequent risks, and mechanisms that will populate drinking water sources and ultimately influence public health and the environment. This critical review provides insights into O₃-biofiltration as a treatment barrier with a focus on development, structure, and composition of the microbial community characteristics involved in the process. The effect of microorganism seeding by the influent before and after the biofilter and ozone oxidation effects are explored to capture the microbial ecology interactions and environmental factors affecting the media ecosystem. The findings of reviewed studies concurred in identifying Proteobacteria as the most dominant phylum. However, Proteobacteria and other phyla relative abundance differ substantially depending upon environmental factors (e.g., pH, temperature, nutrients availability, among others) gradients. In general, we found significant gaps to relate and explain the biodegradation performance and metabolic processes within the biofilter, and hence deserve future attention. We highlighted and identified key challenges and future research ideas to assure O₃-biofiltration reliability as a promising barrier in advanced water treatment applications.