Browsing by Author "de los Reyes, Francis"

Now showing 1 - 5 of 5

Factors Affecting the Formation of Fats, Oils, and Grease Deposits in Sewer Systems and Fate of Fog Deposit Forming Precursors in Sewer Systems
(Water Resources Research Institute of the University of North Carolina, 2012-02) de los Reyes, Francis; Ducoste, Joel J.
Improving startup and operation of anaerobic co-digestion of grease interceptor waste
(NC-WRRI, 2017-07) de los Reyes, Francis; Aziz, Tarek
Improving the Anaerobic Treatment of Sludges and High-Strength Wastewaters through Addition of Electrically-Conductive Particles
(NC WRRI, 2017-07) Call, Douglas; de los Reyes, Francis; Cheng, Qiwen
The growing list of high-strength wastewaters across North Carolina (NC) are well suited for treatment and energy recovery using anaerobic digestion (AD). These include livestock wastes, food wastes, and wastewater-derived sludges that if left untreated, pose risks to NC’s water resources and public health. AD, however, is largely underutilized to treat these wastes. This can be attributed to both economic and technology performance barriers. With respect to performance, one limitation is the operational instability that can arise when syntrophic relationships between key groups of microorganisms in the digester are disrupted; another is the incomplete conversion of organics to methane gas (CH4). To overcome these limitations, we proposed augmenting digesters with electrically conductive microscale particles. These particles have proven effective as conduits for syntrophic microbe-to-microbe direct electron transfer, resulting in improved CH4 generation and waste degradation rates using pure microbial strains in the lab. We hypothesized that supplementing digesters with these materials would result in a similar effect and could provide operators a means to stabilize and improve performance. Our objectives were to experimentally determine the impact of 1) material properties (type, conductivity, size) and 2) particle loading on AD performance. We assessed performance as CH4 generation rates, CH4 recoveries, and organic matter destruction [measured as chemical oxygen demand (COD) removal]. To fulfill our objectives, we supplemented lab-scale, serum bottlebased digesters with different conductive particle types (graphite, biochar, activated carbon) or non-conductive glass (a surface area control) and compared all particle amended bottles with controls lacking particles. We used swine wastewater collected from the NC State Swine Educational Unit as a representative high-strength wastewater. Our results indicate that across all particle types tested, graphite was the most consistent in improving digester performance. Both CH4 production rates and recoveries strongly correlated with the graphite loading rate, reaching a maximum production rate of 30 ± 2.5 mL-CH4/(gVSseed day), which was 34 ± 11% higher than the no-particle control. The other material types did not show clear trends with loadings, and in most cases led to reduced performance relative to the no-particle control. Material electrical conductivity was not found to be a decisive factor for predicting CH4 generation rates. This result was contrary to our expectations. A primary reason was that biochar, and more significantly, activated carbon, strongly adsorbed organic matter from the wastewater. Adsorption was found to have a negative impact on performance. Graphite exhibited little to no adsorptive behavior, resulting in a larger conversion of the initial COD into CH4 gas. Under our conditions tested (single batch cycle; 19 day retention time), the additional CH4 generated with graphite would not recuperate the cost of graphite. Our recommendations moving forward are threefold. First, fundamental investigations of microbial community structure and mechanisms in the presence of conductive versus non-conductive material are needed to determine if the improvements are associated with direct interspecies electron transfer (DIET). Second, alternative means of providing electrically conductive surfaces, such as graphitic brushes or cloths, should be explored, so as to avoid the costs associated with continuous particle amendments. Finally, a broader suite of high-strength wastewaters need to be studied to determine if similar responses as reported here are observed.
Intensification of Anaerobic Digestion: Co-Digestion of Grease Interceptor Waste (GIW) with Thermally Hydrolyzed (TH) Biosolids
(NC Water Resources Research Institute, 2022-07-12) de los Reyes, Francis
Intensifying methane production during anaerobic digestion (AD) is a key factor in making anaerobic digestion economically feasible. We explore two key ideas in biomethane production: using thermally hydrolyzed (TH) biosolids, and co-digestion with grease interceptor waste (GIW). We used modified biochemical methane potential (BMP) tests in several Phases in triplicate: Phase 1 investigated the optimal COD-based substrate to inoculum (S/I) ratio for mono-digestion of TH biosolids and GIW, Phase 2 investigated co-digestion, and Phase 3 investigated codigestion under conditions modified to be more like those of full-scale operations. Application of a TH pretreatment to Phase 1 biosolids, Phase 3 mixed and thickened (M&T) biosolids, and Phase 3 co-substrate (M&T biosolids and GIW) increased the fraction of soluble to total COD by 51.7%, 25.2%, and 25.5%. Modified Gompertz models identified maximum methane potential (MMP) and maximum daily methane production rate (MDMPR). The most productive Phase 1 GIW mono-digestion had a MMP three times that of Phase 1 TH biosolids but had a lag period that was almost seven times longer. In Phase 2 biosolids monodigestions, TH increased MMP and MDMPR in biosolids but no significant effect was observed in GIW. Inclusion of TH GIW and GIW without TH in Phase 2 co-digestions both increased MMP and MDMPR, compared to mono-digestions of biosolids, but there was no significant difference in MMP or MDMPR between these co-digestions. These are consistent with very similar microbial communities at the end of the incubations (analyzed using 16S gene sequencing). Modified Gompertz Model fitting of Phase 3 results also showed no significant difference between TH and raw co-digestions of M&T biosolids and GIW in terms of MMP or MDMPR. Again, these were consistent with the microbial community analysis results, that showed very similar communities at the end of the runs. One reason for the difference in TH effects between Phase 3 and other Phases was the inclusion of primary solids in M&T biosolids. The benefits of TH appeared to be less dramatic in substrates that contained primary solids than in those exclusively composed of waste activated sludge. TH was shown to be beneficial in mono-digestion of waste activated sludge biosolids, more than doubling MMP and increasing MDMPR by more almost seven times. However, TH does not intensify anaerobic digestion when applied to co-substrates of biosolids and GIW. This study found that TH is suitable for application to biosolids at the current state of practice. Incorporation of TH GIW showed no consistent benefit over addition of untreated GIW. The application of TH to GIW does not always lead to increased methane yield or improved digestion kinetics: many factors, including the type of biosolids (WAS vs. primary sludge; thickened vs. unthickened) affect the methane yield.
Tertiary Anammox for Sustainable Nitrogen Removal
(NC Water Resources Research Institute, 2022-04-28) Aziz, Tarek; de los Reyes, Francis; Young, Anthony
Concentrated discharges of nitrogen into our waterways have led to serious environmental impacts, such as eutrophication and algae blooms. Due to these discharges, stringent total nitrogen (TN) discharge limits have been placed on Water Reclamation Facilities (WRFs). Mainstream deammonification offers a novel approach for improving nitrogen removal at these facilities by harnessing anaerobic ammonia oxidizing bacteria (Anammox). However, the success of this process has been limited. Previous research at NC State explored the conversion of tertiary filters to mainstream deammonification filters which were shown to be capable of an average total inorganic nitrogen (TIN) removal rate of 91%, with effluent TIN reaching below 2 mg/L-N. However, this research suggested that nitrate loading concentrations were the limiting factor in meeting 2 mg/L-N TIN effluent limits. Incorporating partial denitrification (PdN), the conversion of nitrate to nitrite for subsequent use in Anammox, offers a promising solution. The goal of this research was to explore the TIN removal capability and feasibility of a PdN-Anammox (PdNA) filter under typical filter loading conditions, in comparison to a conventional denitrification (FdN) filter. Different carbon loading strategies in pilot scale filters confirmed that maintaining a nitrate residual of >1.5 mg-N/L allowed for the highest PdN conversion efficiencies and in turn increased Anammox activity. Furthermore, the carbon requirement (C/N ratio) of 5.1 g COD/g TIN in pilot scale FdN was higher than the 2.08 g COD/g TIN achieved in the PdNA filters, demonstrating the cost benefits associated with mainstream deammonification and the application of PdNA. In addition to greater than 50% reduction in supplemental carbon, other benefits include nearly 38% reduction in oxygen demand and reduction in excess sludge in comparison to conventional BNR processes. Through this pilot study, PdNA was demonstrated to provide TIN removal efficiencies of greater than 80%. With further research, stable TN removal at WRFs at typical filter loading rates can be achieved, and with that, the possibility for substantial operational expenditure (OPEX) savings.