Thompson, Matthew, Thompson

Thompson, Matthew

Matthew Thompson is a Ph.D. candidate in Environmental Engineering at the University of Nebraska -Lincoln and a wastewater EIT at HDR. His research focuses on improving sustainability of wastewater treatment and industrial processes. As an active member with the local Nebraska WEF section for 6 years, he helped with launching the Nebraska WEF section’s mentoring program to help boost student engagement within the water/wastewater profession. A key professional goal of Matt is to help further develop actionable methods and information for sustainable design of wastewater treatment systems. Outside of work, Matt likes to spend time cooking, gardening, and exploring new places with his wife Youra.

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Description: Environmental Life Cycle Assessment of Agriculture Water Reuse From Small Water...

Environmental Life Cycle Assessment of Agriculture Water Reuse From Small Water Resource Recovery Facilities: Case Studies and Spatial-Time-Variant Modeling

Abstract

Introduction
Small water resource recovery facilities (WRRFs) serving communities of less than 10,000 people serve an essential function of treating wastewater to protect public health and the environment but exhibit significant environmental burdens associated with their built infrastructure, electricity use, and direct operating emissions. These systems can play a crucial role in the Food-Energy-Water (FEW) nexus since they help treat water with potential for reuse and can provide nutrient value for agricultural systems. The aging infrastructure of many small WRRFs is needing replacement in the coming decades and will also in many cases require nutrient removal modifications to meet more stringent effluent water quality permit limits to protect freshwater ecosystems (USEPA, 2015). Developing information to determine the conditions in which solutions may be the most cost-effective and environmentally sustainable will be valuable to community leaders, consulting engineers, and state regulators (Verbyla et al., 2013). In analyzing these systems, technologies that employ agricultural water reuse to local cropland can offer a great option for many small communities and thus further research highlighting case studies of their benefits and suitable application could aid in the broader adoption of the technology. The goal of this research was to evaluate the environmental life cycle resource impacts of implementing an agriculture water reuse system for small complete retention lagoons. The objectives of the study were:
(1) to assess the environmental profile tradeoffs of non-discharge lagoons that reuse treated water for non-direct human food consumption agricultural crops;
(2) use historic climate and crop data to model the long-term resource use and environmental impact tradeoffs of operating agriculture water reuse systems for small community lagoons.
Methodology
Life cycle inventory data was collected from 7 existing lagoons within Nebraska that reuse treated wastewater for local agriculture land. Most of the case studies were for communities less than 2,000 people and represented a wide range of climatic conditions from the east to west across Nebraska being representative of semi-humid, arid, and semi-arid climates that influence design and operating performance of lagoon and agriculture systems. A freebody diagram of the agriculture water reuse system is shown in Figure 1. The life cycle inventory collected for the study is shown in Table 1 and included construction, operating electricity usage, water quantity, water quality, and marginal changes occurring on the agriculture land. To help compliment the case study research, a time- and spatial-variant model for agriculture water reuse systems based on water balances was developed to estimate water reuse potential of lagoons and the corresponding resource use and emissions. The design and operation of irrigation lagoons were modeled for locations across the diverse climatic environment of Nebraska using 30 years of historic climate and crop data. Figure 2 shows how the water reuse model was integrated with the LCA model to help estimate potential environmental impacts associated with their use. Table 2 lists the independent variables, source, time step resolution, and spatial resolution utilized for the water reuse model. This included evaporation and precipitation rates, as well as the estimated historic crop evapotranspiration rates. Data on existing lagoon and cropland locations and size were used in assessing the required built infrastructure of the systems. ArcGIS Pro was used for the geospatial assessment of proximity and spatial interpolation of weather data. Assessment of the required built infrastructure, excavation, operating energy use, nutrient value, and potential crop yield improvements are assessed. Background emissions were used from Ecoinvent v3.6 database and used with characterization factors from TRACI 2.1.
Results
Results of the study provide insight into the key factors impacting the sustainability of adopting an agricultural water reuse systems at small WRRFs. Modeling long term performance of these systems helps reveal the implication of water storage, supply, demand, and weather dynamics on water reuse systems. Figure 3 shows the carbon emission intensity of the agriculture water reuse lagoon case studies characterized by source of impacts. Six of the case studies were observed to use water reuse to convert existing dryland cropland to irrigated land whereas one site used water reuse to substitute existing groundwater pumping. In all case studies, adopting agriculture water reuse systems exhibited a net emission reduction. Benefits from excavation reductions, fertilizer reductions, and improvements in crop productivity offset additional resource use with water reuse infrastructure and operating resources. Figure 4a illustrates the 30-year modeled relative max yield percentage of a water reuse system case study that converted dryland cropland to irrigated. On average over time, the water reuse system allowed for 15% increase in crop yields and helped the agriculture land resiliency during a drought year. In Figure 4b, the modeled annual water application rate is plotted relative to differences in crop evapotranspiration and precipitation rates. In this case study, both crop water maximum water demands and effective lagoon water storage capacity were rate limiting factors in how much water is applied. While the quantity of water capable of application to agriculture land is dependent on the relative size of the systems, the effects of low precipitation rates both reduces lagoon water reuse supply capacity and increases that cropland water demands. In the case of systems that use water reuse to help offset existing groundwater pumping for irrigated cropland, environmental impact tradeoffs are largely influenced by relative lagoon/farmland sizing and proximity, and depth of groundwater pumping. Figure 5 shows the change in carbon intensity of adding agriculture water reuse systems to complete retention lagoons based on these variables. Figure 5a shows that for relatively shallow groundwater, using water reuse for agriculture land within a 3-6 km proximity will result in net carbon emission reduction. Figure 5b highlights that sites with significantly deep groundwater will still exhibit net environmental benefits from water reuse at proximities less then 10km. It should be emphasized that these generalizations were based on averages made across 30-years of historic weather data and elevation differences also must be accounted for on a site-to-site basis if they contribute significantly to the pumping head.
Relevance
Provided the large number of small WRRFs throughout the world, wide climatic variability, and need for more sustainable systems, this work helps provide case study data and a framework for analyzing the environmental resource impacts of adopting agriculture water reuse systems. With many small systems experiencing stricter nutrient water quality limits, many are needing to evaluate what technologies may offer the best choice in terms of cost, ease of operability, and environmental performance. Within the context of the FEW nexus, agricultural water reuse from WRRFs will play a key role within small communities and for which its environmental impacts appears highly site-specific, time variable, and can be constrained by both supply and demand dynamics.

With growing global focus on sustainable and resilient systems, this work investigates the environmental life cycle impact of agriculture water reuse employed at small communities. Case study data and spatial-temporal modeling are leveraged to help characterize resource tradeoffs and quantify overall net benefits of water reuse adoption. The influence of site-specific drivers including system sizing and seasonal weather on the supply-storage-demand dynamics within water reuse is explored.

SpeakerThompson, Matthew

Presentation time

15:30:00

15:55:00

Session time

15:30:00

17:00:00

TopicFundamental Level, Small Communities and Decentralized Systems, Utility Management and Leadership

Author(s)

Thompson, Matthew

Author(s)Matthew Thompson1; Bruce Dvorak2

Author affiliation(s)HDR, Omaha, NE1; University of Nebraska-Lincoln, Lincoln, NE2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2022

DOI10.2175/193864718825158687

Volume / Issue

Content sourceWEFTEC

Word count20

Getting a Grip on AGS Waste Solids: Settleability and Phosphorus Release

Abstract

INTRODUCTION The Aerobic Granular Sludge (AGS) and other densified processes offer the promise of biomass intensification with the added benefit of nutrient removal. A key element needed to support AGS is the selective wasting of flocculant biomass and particles from the process. Wasting occurs from the top of the settled solids or by other physical methods (e.g. hydrocyclones). While this wasting approach is essential to the AGS process, it results in waste solids (WAS) streams that differ from conventional activated sludge (CAS) with higher flow rates, lower total suspended solids (TSS) concentrations, and biological nutrient removal (BNR) activity. Therefore, the AGS WAS must be managed in a completely different way from CAS WAS. Two key WAS management challenges need to be considered. The first challenge is managing intermittent AGS WAS flows, which are on the order of 5 to 15 times higher than CAS WAS flow rates on average and approaching 100 times higher for instantaneous flow rates. The second challenge for AGS WAS management is understanding the impact of the phosphorus accumulating organisms (PAOs) on the solids handling system and managing the potential for struvite formation. The objectives of the project work are the following: *Define AGS WAS settleability characteristics *Expand the understanding of phosphorus release potential (total OP release) and rates METHODS & APPROACH Solids Settling Characterization All WAS samples were taken directly from the pipe that transfers WAS from the AGS reactors to the solids buffer tank (Figure 1). Settlability was evaluated using a 5.5-inch diameter column settler (Figure 2). The settling column was filled with 10 L of WAS sample for each test. Sample ports, located every 2 L and at the bottom of the column, were used to collect supernatant and settled solids samples. Settled WAS and supernatant samples were taken and TSS was measured in both samples. Sludge volume index (SVI) values were also estimated. Phosphorus Release Rates and Potential Phosphorus release testing has been conducted using gang stirrer apparatuses with 1.5 L samples (Figure 3) and low-rate mixing (30-50 s-1). A carbon source was added to 10 of the samples giving F:M ratios ranging from 0.0 to 0.5 g-COD/g-VSS. Additionally, the initial TSS concentration was varied by providing some initial thickening in some samples resulting in a range from 1,500 to 5,000 mg/L. The initial total phosphorus and phosphate concentrations were measured in the raw WAS sample. Samples were subsequently taken from the release tests through a 34 h time period. Samples were filtered and phosphate measured. Results & Discussion AGS WAS Settling Rates The WAS volume was recorded as a function of time by measuring the depth of the sludge layer in two separate test batches. Initial WAS concentrations were 2,500-5,000 mg/L and thickened to 8,500-10,000 mg/L by the end of the test period. The final settled volume was reached within 4-12 minutes. The maximum settling velocity was 3.9-11.9 m/hr at time 2-4 minutes and decreasing over time (Figure 4). SVI5 values were estimated in the range 110-200 mL/g, and SVI30 values were calculated in the range 100-120 mL/g. The TSS concentration in the supernatant was 8-40 mg/L. Evaluation of modeled settling in a clarifier was conducted using a BioWin simulator based on the calculated Vesilend model clarifier coefficients. Model sludge blanket height and effluent suspended solids remained within the desired range, even with the additional solids. A state point analysis from BioWinTM indicated that the AGS WAS operating condition was within the solids-flux limitation of the clarifier (Figure 5). Phosphorus Release Rates and Potential Phosphorus release testing showed phosphorus release rates varied initially in response to carbon dosing with higher short-term release rates followed by reduced long-term release rates (Figure 7). Short-term (or initial) release rates varied from 0.4 mg-P/g-TSS/h for no carbon addition to 4.0 mg-P/g-TSS/h for carbon addition (acetic acid with F:M of ~ 0.4 g/g). The long-term release rates varied from 0.1 to 0.7 mg-P/g-TSS/h for initial TSS concentrations in the range 1,500-5,000 mg/L (Table 1 and Figure 8). The effect of starting TSS concentration was more important than carbon addition for this test batch with rates normalized to volume increasing exponentially as shown in Figure 8. The overall phosphorus released varied in the range 7-22% of the initial TP measured. A follow-up test was conducted showing a release of 25-30% of the initial TP over a 72-h release period. A phosphorus mass balance on the plant aligns with maximum releasable TP observed based on the phosphorus removed from the liquid stream. An evaluation of the settling characteristics of AGS WAS showed high settling velocities resulting in WAS TSS concentrations similar to CAS WAS TSS concentrations with low DSS concentrations. Based on the results of phosphorus release testing, struvite mitigation is recommended for anaerobic digestion of AGS WAS.

The aerobic granular sludge (AGS) process offers strong potential for both incorporating nutrient removal and process intensification for wastewater treatment. Some outstanding research needs have come to the forefront. This paper seeks to address questions that have arisen regarding waste solids. In particular, the work evaluated the settleability and phosphorus release potential of AGS waste solids.

SpeakerEvans, Eric

Presentation time

14:00:00

14:30:00

Session time

13:30:00

15:00:00

SessionEvaluating Plantwide Impacts of AGS and DAS

Session number606

Session locationRoom 343

TopicIntermediate Level, Municipal Wastewater Treatment Design, Nutrients, Research and Innovation

Author(s)