2020 Projects

The intensification of anaerobic digestion (AD) of biosolids is a major goal and important factor in making anaerobic digestion economically feasible. This project explores two key ideas in significantly intensifying biomethane production in anaerobic digesters at water resource recovery facilities: using thermally hydrolyzed (TH) biosolids, and co-digestion with grease interceptor waste (GIW). Both are approaches that allow increased organic loading rates per unit volume of reactor, and separately have been the focus of research in the last few decades. This project is among the first to study how TH processes and GIW co-digestion can be combined to further increase the intensification of methane production. A lab-scale TH unit will be constructed, and a series of biomethane potential (BMP) tests will be used to determine the optimal substrate-to-inoculum ratio for combined TH biosolids + GIW co-digestion. By comparing various combinations of single and co-substrates and using kinetic modeling, differences in anaerobic digestion performance can be characterized. Lab-scale anaerobic digesters will be operated to determine the highest level of GIW addition in co-digestion with TH biosolids without inhibition of methanogenesis. Microbial community analysis using next-generation sequencing approaches will allow characterization of the microbial populations in the various combinations of co-substrates. Initial analysis of the co-digested sludge, including effects on dewaterability and coliform levels will also be conducted. The results of this study will inform design and operation of anaerobic digesters, generating insights that can be used in full-scale implementation of anaerobic co-digestion of GIW and TH biosolids in utilities in NC and around the country.

The adhesion of fat, oil, and grease (FOG) deposits in sewer pipes causes 25% of the Sanitary Sewer Overflow (SSOs) in the USA. Additionally, the sewer collection system in the U.S is old and requires replacement or renovation. One potential solution to the FOG deposit accumulation challenges in the collection systems is to design new sustainable sewer line construction materials that reduces the adhesion of these deposits on sewer pipe walls. Previous research has only reported the FOG deposit formation mechanism and the factors affecting those formations. Yet, no research has been performed to understand the FOG deposits adhesion mechanism. This study provides an improved understanding of the FOG deposit adhesion mechanism inside sewer lines by testing various materials, i.e., concrete, PVC, granite, limestone, and porous ceramic materials for a 30-day FOG deposit adhesion test. The test materials were prepared by varying a number of surface properties such as surface roughness, porosity, pH, and surface chemical composition. After analyzing the FOG deposit adhesion test results on various test materials, research results revealed that only the sewer line materials containing calcium as a strong electropositive Lewis acid bonding sites resulted in the FOG deposit adhesion on their surface. In addition, samples having high surface roughness, pH, and porosity also resulted in higher FOG deposit accumulation on their surfaces. The FTIR analyses of FOG deposits formed on different sewer line materials showed that a high fraction of saponified calcium soaps were formed on concrete samples. Moreover, the percent soap content of the FOG adhered on concrete samples exhibit a spatial variation with the layer adjacent to the concrete surface had a higher percentage saponification (82%) compared to the layer adjacent to the wastewater interface (38%). The result of this study encourages municipalities to avoid the use of sewer system cleaning process that damages the surface of sewer lines and introduces additional surface roughness. Also, a regular cleaning of sewer lines is encouraged to avoid the FOG build-up by rinsing the weakly adhered FOG deposits.

With a large percentage of US population residing in arid areas, indirect potable water reuse is becoming a widespread practice. Among the pioneering states are California and Colorado, where drinking water treatment plants acknowledge the contribution of treated wastewater effluent to their source water and purposefully include this source in their water supply planning. On the other hand, many areas that have no necessity to include reuse water in the potable supplies still practice the unacknowledged, or so-called “de facto” potable water reuse when a drinking water treatment plant is located downstream of a wastewater treatment plant. Due to public opposition to direct potable reuse, an environmental buffer (river, aquifer or reservoir) is frequently in place to mitigate the “toilet-to-tap” perception. The goal of this study is to evaluate the effectiveness of the environmental buffers for water quality improvement. Samples will be collected from potable water reuse systems (acknowledged or de facto) that utilize a variety of environmental buffers: wetlands, groundwater recharge, riverbank filtration, river and reservoir/lake. Multiple contaminant classes will be analyzed (salts, metals, pharmaceuticals, antibiotic resistance genes, pesticides/herbicides, nutrients, microorganisms, suspended solids and organic carbon) to determine whether the environmental buffers reduce or increase the contaminant load at the drinking water treatment facility. It is anticipated that while some contaminants may get attenuated in the environment (nutrients), some may get reintroduced (pesticides and herbicides, suspended solids, microorganisms), potentially resulting in a higher cost of treatment with an environmental buffer than without it. Additionally, environmental buffers allow contact between trace antibiotics in wastewater effluent and microorganisms – a phenomenon linked to the development of antibacterial resistance in the environment. An environmental buffer may also allow some attenuation of emerging contaminants, and different pathways will be evaluated: photolysis, adsorption and biodegradation. The best management practice recommendation will be proposed as a result of this research that would include the pros and cons of environmental buffers, the effectiveness of different types of buffers for attenuation of various contaminant classes, and estimated difference in the water reuse treatment cost with and without different types of environmental buffers.

Our project, Multidimensional Assessment of North Carolina Community Water System Vulnerabilities, assessed the nature and distribution of vulnerabilities in North Carolina community water systems through achievement of two objectives. First, we developed a network-based method for assessing interrelationships among water system vulnerabilities and used expert information and data from several sources to apply the method to North Carolina water systems. Our measurement of water system characteristics relied on population data estimated from a newly generated digitized statewide map of water system service area boundaries developed in collaboration with the Water Supply Planning Branch at the Division of Water Resources (DWR). Applying our multicriteria approach to 319 North Carolina water systems, we found that vulnerabilities are dispersed: poor performance on one dimension, especially compliance with safe drinking water regulations, does not indicate poor performance on other dimensions. We also found that financial vulnerabilities are correlated with economic conditions in the communities served—in particular, water systems struggling to meet their debt obligations tended to serve disproportionately low-income populations. Second, we used web scraping and automated data processing to measure and analyze the signals that the public receives about water system performance through news coverage of boil advisories, water main breaks, and other service disruptions. We found that coverage of service disruptions as a proportion of overall news coverage has not increased over time. Although coverage rises during severe weather, the most common news attention to infrastructure failure is not tied to weather, planned disruption, or human error—instead, it seems to signal the deterioration we would expect to see in aging systems. We carried out our work while the State Water Infrastructure Authority and the Local Government Commission were developing the Viable Utility Program and used much of the same data. Our purpose was different, however: whereas the Viable Utility Program seeks to identify particular utilities in need of assistance, our aim was to identify patterns in vulnerabilities across water systems to inform policy-making that addresses multiple systems. Overall, our results demonstrate the tradeoffs that water systems face in balancing affordability against the capacity to deliver drinking water reliably over the long term, especially in low income communities. Our findings also indicate that fiscally distressed water systems are performing by other measures similarly to non-distressed small utilities, suggesting that financial support could go far in improving water system performance.

Anthropogenic nutrient loading is a critical driver of water quality throughout
North Carolina and much of the world. Nutrient loading has increased over the last century due to fertilization of crops and green spaces, as well as waste from humans, pets, and livestock. The most salient outcome of nutrient loading is increased eutrophication (organic matter accumulation in surface waters), often leading to harmful algal blooms and hypoxia, which jeopardize water supplies and public recreation. As such, developing nutrient criteria and management strategies is a timely objective for state water resources managers. While sources of nutrients have been identified and many nutrient control measures have been proposed, there remains a need to quantitatively assess these sources and controls, particularly at the watershed scale. In this study, we propose a modern, data-driven approach to update our knowledge of the magnitudes of various sources and the effectiveness of various nutrient control strategies. The approach leverages large databases of water quality, hydro-meteorology, and watershed attributes, which have been developed by federal, state, and local governments over the last few decades. The approach will also leverage and advance a sophisticated “hybrid” watershed model that combines a mechanistic representation of nutrient fate and transport within a probabilistic (Bayesian) framework where prior knowledge of loading and transport rates is updated through data-driven inference, and where uncertainty is rigorously quantified. Our project will focus on the Falls and Jordan Lake watersheds of North Carolina, for which preliminary models and data are already available. Key objectives of the proposed research include (1) development of an integrated geospatial database on watershed development, (2) adaptation of the hybrid watershed model to assess watershed development practices, and (3) application of the model to assess future management scenarios. Expected outcomes include quantitative guidance for developing nutrient reduction goals and watershed management strategies.

Concentrations of the earthy/musty taste/odor compounds geosmin and MIB (2- methylisoborneol) annually exceed the threshold of human detection (~10 ng/L) in key drinking water reservoirs in Durham County, specifically Lake Michie. This causes a notable rise in customer complaints to City of Durham Water Management Department (CDWMD), especially in late Spring and Summer, and a perception that drinking water quality is poor. The microbial source(s) of these taste & odor (T&O) compounds is assumed; thus targets for effective monitoring and mitigation are not well-established. Recent phytoplankton monitoring, via flow cytometry (FCM) and microscopy, suggests picocyanobacteria (PicoC; cyanobacteria <3 µm diameter) have a role in elevated geosmin concentrations in Spring and early Summer– an intriguing result as PicoC’s are often overlooked as geosmin sources. In summer –filamentous cyanobacteria are more prevalent and may contribute to high geosmin and MIB levels during this time of the year. CDWMD uses copper-sulfate based algicide to reduce cyanobacterial biomass and T&O but the effectiveness of the treatment and whether reduced application could better aid T&O mitigation is unknown. It is hypothesized that: (H1) high net growth of PicoC is linked to geosmin peaks in Spring, while filamentous cyanobacteria are key producers in Summer; (H2) PicoC and filamentous cyanobacteria are the most prevalent geosmin producers in LM; (H3) reduced algicide addition will have a bacteriostatic effect – where cyanobacteria are not extensively lysed and concentrations of T&O compounds in the dissolved phase are reduced. H1 will be tested via improved time-series monitoring of phytoplankton (PicoC, filamentous cyanobacteria) and concentrations of T&O earlier in the phytoplankton growth season. H2 will tested using metagenomic sequencing of Lake Michie plankton DNA to directly identify populations possessing geosmin or MIB synthase genes. Last, algicide gradient addition experiments will be performed to test H3. Expected outcomes include: (1) establishment of phytoplankton targets for future monitoring and/or prediction of elevated T&O concentrations and (2) an evaluation of reduced algicide addition as an approach for water managers to lower dissolved T&O compound levels and save on costs. An educational outcome of the project will be T&O teaching modules that convey basics of what compounds are involved and who produces them to the general public. The module will be implemented as part of an ongoing ‘mobile laboratory’ outreach program (called MAML) at Lake Johnson, Raleigh, and will include pre- and post-questionnaires to assess the effectiveness of these modules.

Storm events are expected to increase with climate change, with the potential to adversely impact environmental quality and public health. Extreme flooding associated with storms including the recent flooding from Hurricane Florence often causes loading of contaminants to water resources. Using a One Health framework that recognizes that human, animal, and environmental health are
inextricably linked, this study will assess impacts of Hurricane Florence on water quality in areas of dense food animal production. We aim to (1) measure microbial water quality at sites proximal to hog confined animal feeding operations and control sites, (2) compare levels of environmental antimicrobial resistance (environmental AMR) at study sites, and (3) model spatial distributions of contaminants and associated environmental hazards in areas of dense food animal production. This research will include analysis of samples collected both before and after Hurricane Florence so that we can evaluate hurricane-related impacts. Our analysis will include innovative assessments of environmental AMR, as well as the development of spatial-temporal models to help identify factors important or protective to the spread of contaminants. These models will also provide valuable insight into appropriate methods for modeling exposure to industrial hazards more generally and can help inform emergency management protocols. Project results will help clarify the effects of extreme flooding on environmental contaminant transport and can inform strategies for waste management, antibiotic use, and one health surveillance. Ultimately, this work will lead to more resilient agricultural systems and communities better prepared to weather the storms that frequent the North Carolina coast.