Development of Novel Bioelectrochemical Systems for in Situ Nitrate Removal from Groundwater

This study aims to develop new approaches for in situ nitrate removal from groundwater by using bioelectrochemical systems (BES). BESs employ bioelectricity generated from organic compounds to drive nitrate moving from groundwater into the electrode chamber and reduce nitrate to nitrogen gas by heterotrophic denitrification. In first phase experiments, nitrate ions were driven into the anode chamber of a de-coupled reactor, whose electrode chambers were separated, where heterotrophic denitrification took place with organic reduction. It was proved that by applying additional electrical potential at 0.8V, the reactor could achieve highest removal rate of 208.2±13.3 g NO3--N/m3/d, when initial nitrate concentration in synthetic groundwater well is around 20 mg/L. Removal rate appeared a linear relationship with the initial nitrate concentration in groundwater. Electricity not only enhanced nitrate removal rate but also could inhibit ion exchange and prevent introducing other undesired ions into groundwater. In second phase experiments, the BES reactor was modified to single tubular. Nitrate ions transport across anion exchange membrane (AEM) into a mid-chamber between anode chamber and cathode, where they were concentrated and finally lead into anode chamber to be biological denitrificated. The slower mid-chamber water flowing, the less cost would be for operation and the flow rate affect slightly to nitrate transport. It was found that nitrate concentration could reach equilibrium after about 17 hrs. Protons produced from cathode reaction were more likely travel across AEM into mid-chamber, which restricted nitrate ions\u27 movement. The BES was also proved feasible when applying in real groundwater and tended to produce more coulomb of charge. Further development of this BES will need to address several key challenge

Micropollutant-Free Nutrient Recovery: Adsorption of Micropollutants on Ion Exchangers and Biosolids-Derived Biochar

The presence of excessive nutrients in treated wastewater effluent is a growing concern in terms of water quality and ecological balance. Thus, removal of nutrients is of great interest. Moreover, the removed nutrients can be recovered in forms amenable for agricultural reuse, which yields a sustainable supply of nonrenewable phosphorus that can be used to support global food production. As nutrient recovery gains interest, it is essential that the products be free of harmful contaminants. One class of contaminants of great concern is organic micropollutants. To help address these issues, this study evaluated the fate and impact of micropollutants during nutrient recovery via an ion exchange-regeneration-precipitation process. The adsorptive behavior of the micropollutants was evaluated for the ion exchangers and for a sustainable biosolids-derived biochar that may be useful for separating micropollutants from nutrients prior to ion exchange. Bench-scale batch reactors were operated for ion exchange-regeneration and adsorption tests. The surface properties of ion exchangers and biochar were characterized to help assess the mechanisms of micropollutant adhesion on solid adsorbents. The presence of micropollutants in water reduced the kinetic rates of nutrient exchange onto ion exchangers. Micropollutants were adsorbed to the phosphate exchangers and were released with phosphate ions during ion exchange regeneration. To remove micropollutants from water prior to ion exchange, biosolids-derived biochar was used since micropollutants were adsorbed to the biochar, but ionic nutrients were not. Biochar produced at higher pyrolysis temperatures increased adsorption capacity, as did higher ambient temperatures for batch sorption experiments. Under multi-solute conditions, not all target micropollutants demonstrated suppressed adsorption. Biochar, ammonium, and phosphate exchangers were accordingly arranged in sequence in a flow-through system. The biochar column removed more than 80% of influent hydrophobic micropollutants and 50% of hydrophilic micropollutants, thereby reducing the presence of micropollutants in the nutrient removal/recovery process. Thermodynamic parameters indicated an endothermic adsorption reaction and heterogeneity in adsorption site distribution on the biochar surface. The binding energy and entropy change of adsorption were not affected by the presence or absence of other solutes in the matrix. The underlying binding mechanism for biosolids-derived biochar adsorption was potentially dominated by non-specific hydrophobic interaction and non-covalent interaction including hydrogen bonding and π-stacking

Triclosan Adsorption Using Wastewater Biosolids-derived Biochar

Organic micropollutants are ubiquitous in the environment and stem from municipal wastewater treatment plant discharges. Adsorption can be used as a tertiary treatment to complement the conventional activated sludge process to remove micropollutants prior to discharge. This research evaluated the performance of wastewater biosolids-derived biochar as an adsorbent to remove triclosan from water. Pre-conditioning of the biochar using hydrochloric acid (HCl) was an essential step for triclosan adsorption. Using acid-conditioned biochar, maximum adsorption of 872 μg triclosan per g biochar was achieved with biochar produced at 800 °C. Biochar produced at higher pyrolysis temperatures tended to have higher triclosan sorption capacity using initial triclosan concentrations of 200 μg L−1 levels. However, pyrolysis temperature had less impact on triclosan sorption at lower, environmentally relevant concentrations. Low solution pH (3) enhanced adsorption and high pH (11) inhibited adsorption. Effective triclosan sorption was observed between pH 5 and 9, with little variation, which is positive for practical applications operated at near-neutral solution pH. In wastewater, acid-treated biochar also effectively sorbed triclosan, albeit at a decreased adsorption capacity and removal rate due to competition from other organic constituents. This study indicated that adsorption may occur mainly due to high surface area, hydrophobicity, and potential interaction between biochar and triclosan functional groups including hydrogen bonding and π-stacking. This work demonstrated that acid-conditioned biosolids-derived biochar could be a suitable sorbent to remove triclosan from wastewater as a final polishing treatment step

Fate and Impacts of Triclosan, Sulfamethoxazole, and 17β-estradiol during Nutrient Recovery via ion Exchange and Struvite Precipitation

Increasing emphasis on resource recovery from wastewater highlights the importance of capturing valuable products, e.g., nutrients such as nitrogen and phosphorus, while removing contaminants, e.g., organic micropollutants. The objective of this research was to evaluate the fate of the micropollutants triclosan (present as a mixture of neutral and anionic species at neutral pH), 17β-estradiol (neutral at neutral pH), and sulfamethoxazole (anionic at neutral pH) during nutrient recovery using ion exchange-precipitation. Adsorption of the three micropollutants to the phosphate-selective ion exchange resins LayneRT and DOW-HFO-Cu ranged from 54% to 88% in Milli-Q water tests and 50% to 71% in wastewater tests using anaerobic effluent. The micropollutants did not sorb to the ammonium-selective exchanger, clinoptilolite. The presence of the micropollutants reduced the kinetic rates of nutrient exchange onto ion exchangers. However, the micropollutants did not interfere with nutrient capacity on the ion exchangers, likely due to the low concentration of micropollutants and potentially different mechanisms of adsorption (i.e., Coulombic and non-Coulombic attractions for micropollutants) compared to the target ions. Micropollutants that sorbed to the phosphate exchangers were released with phosphate ions during regeneration. Concentrations of NaOH and NaCl in regeneration solutions did not correlate with micropollutant desorption. Among the micropollutants studied, the more hydrophobic triclosan and 17β-estradiol adsorbed to the resins to greater extents. These compounds also demonstrated lower desorption rates than sulfamethoxazole during regeneration in Milli-Q water tests. Batch struvite precipitation tests revealed that the micropollutants were not enmeshed in precipitated struvite crystals nor sorbed during crystallization, indicating that the struvite product was free of triclosan, 17β-estradiol, and sulfamethoxazole

Biosolids-Derived Biochar for Triclosan Removal from Wastewater

Micropollutants, including antibiotics, hormones, pharmaceuticals, and personal care products, are discharged into the environment with liquid and solid effluent streams from water resource recovery facilities (WRRFs). The objective of this research was to determine whether biosolids-derived biochar (BS-biochar) could be used as a sorbent in continuous flow-through columns to remove micropollutants as a polishing step for wastewater treatment. Triclosan (TCS) was selected as a representative micropollutant due to frequent detection in liquid effluents, residual biosolids, and surface waters. Bench-scale column experiments were conducted to determine the effect of flow rate and competition due to the presence of other organic micropollutants and inorganic nutrients on TCS adsorption to BS-biochar. TCS removal efficiency was compared in Milli-Q water and secondary wastewater effluent by using two commercial adsorbents: a granular activated carbon and a wood-based biochar. Increased removal of TCS was observed at lower flow rates (2.6 gpm/ft2) compared with higher flow rates (10.3 gpm/ft2). Presence of inorganic nutrients (NH4+ and PO43−) and organic micropollutants 17β-estradiol and sulfamethoxazole decreased adsorption of TCS to BS-biochar. TCS was sorbed to BS-biochar in wastewater, but percent removal decreased in wastewater relative to Milli-Q water. This study demonstrated that BS-biochar can remove TCS from wastewater in continuous flow-through columns, although to a lesser extent than activated carbon. An additional benefit of using BS-biochar is that WRRFs could re-activate biochar on-site by using a pyrolysis reactor

Ion Exchange for Nutrient Recovery Coupled with Biosolids-Derived Biochar Pretreatment to Remove Micropollutants

Wastewater, especially anaerobic treatment effluent, contains high ammonia nitrogen (NH4-N) and inorganic orthophosphate (PO4-P), which necessitate additional treatment to meet stringent discharge regulations. Ion exchange regeneration is a process that can be adopted for not only removing but also recovering nutrients. However, recovering nutrients by ion exchange from nutrient-rich effluents that also contain micropollutants (which typically pass through anaerobic treatment as well) may result in subsequent problems, since micropollutants could end up in ion exchange effluent, regenerant, or recovered fertilizer products. Micropollutant removal by a nonselective adsorbent, such as biosolids-derived biochar, before nutrient recovery processes would mitigate potential risks. The objective of this research was to evaluate the capability of biosolids-derived biochar as a pretreatment step for separating micropollutants from nutrient-rich water before ion exchange for nutrient recovery. In the presence of ammonium and phosphate, both pristine and regenerated biosolids-derived biochar could effectively adsorb triclosan (TCS) and estradiol (E2), and to a lesser extent, sulfamethoxazole (SMX) in batch sorption experiments. On the other hand, nutrient ions were not effectively adsorbed by biosolids-derived biochar. A continuous flow-through system consisting of columns in series filled with biochar, LayneRT, and then clinoptilolite was operated to test selective removal of micropollutants and nutrients in a flow-through system. The biochar column achieved more than 80% removal of influent TCS and E2, thereby reducing the chances of micropollutants being adsorbed by ion exchangers. Sulfamethoxazole removal through the biochar column was only 50%, indicating that biosolids-derived biochar would have to be optimized in the future for hydrophilic micropollutant removal. Influent nutrients were not effectively removed by the biochar column, but were captured in their respective selective ion exchanger columns. This research revealed that biosolids-derived biochar could be employed before ion exchange resins for removal of micropollutants from nutrient-rich water

Adsorption of Organic Micropollutants to Biosolids-Derived Biochar: Estimation of Thermodynamic Parameters

This research quantified thermodynamic parameters to better understand the use of wastewater biosolids-derived biochar as an adsorbent to remove micropollutants. The objective of this research was to quantify adsorption capacity; isosteric heat; and change of enthalpy, entropy, and free energy characterizing adsorption reactions between biochar and micropollutants. Adsorption isotherms were developed using a range of temperatures for the micropollutants benzyldimethyldecylammonium chloride (BAC-C10) Carbamazepine (CBZ), 17β-estradiol (E2), 17α-ethynylestradiol (EE2), and triclosan (TCS). The thermodynamic parameters derived from the isotherm data were used to assist in characterizing binding affinity, spontaneity, and mechanisms of adsorption. More polar compounds such as BAC-C10 and CBZ exhibited linear adsorption, indicating weak interactions with more polar amorphous moieties on the biochar surface. For the micropollutants that were present predominantly in the neutral form at pH 7 (CBZ, E2, EE2, and TCS), increasing hydrophobicity increased the extent of adsorption. The enthalpy change of adsorption and the positive correlation between hydrophobicity and change of entropy (R2=0.8) both suggest that hydrophobic interaction was the dominant adsorption mechanism for neutral compounds. Increases in adsorption with increasing temperature, together with the estimated thermodynamic parameters, indicated that the reactions were endothermic, meaning that higher temperatures should offer improved removal via adsorption. The negative free energy changes observed suggested that adsorption was spontaneous and that adsorption rates outcompete desorption rates. Under multi-solute conditions, the adsorption capacities for all compounds were suppressed to varying extents; however, the magnitude of changes in enthalpy and entropy were not affected by competitive multi-solute adsorption

Characteristics and Applications of Biochars Derived from Wastewater Solids

Pyrolysis is a thermochemical decomposition process that can be used to generate pyrolysis gas (py-gas), bio-oil, and biochar as well as energy from biomass. Biomass from agricultural waste and other plant-based materials has been the predominant pyrolysis research focus. Water resource recovery facilities also produce biomass, referred to as wastewater solids, that could be a viable pyrolysis feedstock. Water resource recovery facilities are central collection and production sites for wastewater solids. While the utilization of biochar from a variety of biomass types has been extensively studied, the utilization of wastewater biochars has not been reviewed in detail. This review compares the characteristics of wastewater biochars to more conventional biochars and reviews specific applications of wastewater biochar. Wastewater biochar is a potential candidate to sorb nutrients or organic contaminants from contaminated wastewater streams. While biochar has been used as a beneficial soil amendment for agricultural applications, specific research on wastewater biochar is lacking and represents a critical knowledge gap. Based on the studies reviewed, if biochar is applied to land it will contain less organic micropollutant mass than conventional wastewater solids, and polycyclic aromatic hydrocarbons are not likely to be a concern if pyrolysis is conducted above 700 °C. Wastewater biochar is likely to serve as a better catalyst to convert bio-oil to py-gas than other conventional biochars because of the inherently higher metal (e.g., Ca and Fe) content. The use of wastewater biochar alone as a fuel is also discussed. Finally, an integrated wastewater treatment process that produces and uses wastewater biochar for a variety of food, energy, and water (FEW) applications is proposed

Towards Building the Federated GPT: Federated Instruction Tuning

While "instruction-tuned" generative large language models (LLMs) have demonstrated an impressive ability to generalize to new tasks, the training phases heavily rely on large amounts of diverse and high-quality instruction data (such as ChatGPT and GPT-4). Unfortunately, acquiring high-quality data, especially when it comes to human-written data, can pose significant challenges both in terms of cost and accessibility. Moreover, concerns related to privacy can further limit access to such data, making the process of obtaining it a complex and nuanced undertaking. Consequently, this hinders the generality of the tuned models and may restrict their effectiveness in certain contexts. To tackle this issue, our study introduces a new approach called Federated Instruction Tuning (FedIT), which leverages federated learning (FL) as the learning framework for the instruction tuning of LLMs. This marks the first exploration of FL-based instruction tuning for LLMs. This is especially important since text data is predominantly generated by end users. Therefore, it is imperative to design and adapt FL approaches to effectively leverage these users' diverse instructions stored on local devices, while preserving privacy and ensuring data security. In the current paper, by conducting widely used GPT-4 auto-evaluation, we demonstrate that by exploiting the heterogeneous and diverse sets of instructions on the client's end with the proposed framework FedIT, we improved the performance of LLMs compared to centralized training with only limited local instructions. Further, in this paper, we developed a Github repository named Shepherd. This repository offers a foundational framework for exploring federated fine-tuning of LLMs using heterogeneous instructions across diverse categories.Comment: Project page: https://github.com/JayZhang42/FederatedGPT-Shepher