Journal of Environmental Engineering

The effect of nitrate (${\mathrm{NO}}_3^{-}\text{-}\mathrm{N}$) concentration in catholyte on electricity generation and pollutant removal was investigated in biocathode microbial fuel cells (BMFCs). Results indicated that the ${\mathrm{NO}}_3^{-}\text{-}\mathrm{N}$ removal rate and output voltage could be promoted with increasing ${\mathrm{NO}}_3^{-}\text{-}\mathrm{N}$ concentrations, but both of them would be inhibited when the ${\mathrm{NO}}_3^{-}\text{-}\mathrm{N}$ concentrations was more than $100.0\mathrm{mg}/\mathrm{L}$. The maximum ${\mathrm{NO}}_3^{-}\text{-}\mathrm{N}$ removal rate and the maximum output voltage was $0.833\mathrm{mg}/(\mathrm{L}/\mathrm{h})$ and 406 mV, respectively, when the initial ${\mathrm{NO}}_3^{-}\text{-}\mathrm{N}$ concentration was $100.0\mathrm{mg}/\mathrm{L}$. Based on the Han–Levenspiel model, the kinetics of ${\mathrm{NO}}_3^{-}\text{-}\mathrm{N}$ removal and output voltage were established in which the maximum ${\mathrm{NO}}_3^{-}\text{-}\mathrm{N}$ removal rate was $1.06\mathrm{mg}/(\mathrm{L}/\mathrm{h})$, and the maximum output voltage was 478 mV. Moreover, ${\mathrm{NO}}_3^{-}\text{-}\mathrm{N}$ concentrations had a great impact on the coupling of electricity generation and ${\mathrm{NO}}_3^{-}\text{-}\mathrm{N}$ removal, which indicated that electricity generation was closely related to the ${\mathrm{NO}}_3^{-}\text{-}\mathrm{N}$ removal. In addition, it was found that the community structure in the cathode biofilm by high-throughput sequencing changed at different ${\mathrm{NO}}_3^{-}\text{-}\mathrm{N}$ biofilm as measured by the main functional microbial genus responsible for removing ${\mathrm{NO}}_3^{-}\text{-}\mathrm{N}$, which remained as denitrifying Proteobacteria.

Soils in the San Joaquin Valley of California have been a source of selenium (Se) release through dissolution into agricultural drainage, requiring treatment before discharge to the environment. A full-scale primarily anaerobic, granular activated-carbon (GAC) bioreactor with an empty bed contact time ranging from 3.4 to 5.0 h was fed $757\mathrm{L}/\min$ of second-pass agricultural drainage water (ADW) at the San Luis Demonstration Treatment Plant (SLDTP) in Firebaugh, California, for 1,062 days. This study summarized startup of an actual water treatment plant with a process scheme that had never been designed or operated at this scale. ADW nitrate (${\mathrm{NO}}_3^{-}$) and dissolved oxygen (${\mathrm{O}}_{2(\mathrm{aq})}$) concentrations largely dictated the externally dosed carbon (EDC), or glycerin dose, which served as the electron donor to achieve selenate (${\mathrm{SeO}}_4^{2-}$) reduction to elemental Se (${\mathrm{Se}}^0$). Total Se (${\mathrm{Se}}_{\mathrm{T}}$) influent concentrations between 111 and $332\mu \mathrm{g}/\mathrm{L}$ were treated to average effluent ${\mathrm{Se}}_{\mathrm{T}}$ concentrations of $7.4\mu \mathrm{g}/\mathrm{L}$ across the bioreactor. Bioreactor effluent ${\mathrm{Se}}_{\mathrm{T}}$ concentrations were further reduced across a downstream ultrafiltration membrane system (UFMS) to an average permeate ${\mathrm{Se}}_{\mathrm{T}}$ concentration of $2.9\mu \mathrm{g}/\mathrm{L}$. It was determined that most of the ${\mathrm{Se}}_{\mathrm{T}}$ removed from the ADW was retained on the bioreactor GAC and was not amenable to removal through backwashing, rendering it hazardous waste by both California and federal standards. Removal of other trace metals such as chromium and uranium were investigated.

Chromates are widely used for their anticorrosive properties. Unfortunately, they are hazardous, with environmental agencies regulating their levels to below 10 parts per billion (ppb) in drinking water. Because single-use anion-exchange resins are the standard tools for chromate removal, accurate predictive dynamic models are necessary for quick decisions based on deviations of the inlet concentration to achieve the desired outlet purity requirements. To this end, we studied various dynamic models to simulate the ion exchange process for targeted chromate removal. Of those studied, we selected the Thomas model for its accuracy. The Thomas model has two parameters, which are estimated via minimization of the sum of square errors between the predicted model and the experimental data set with varying process conditions. In these analyses, the resulting model demonstrated large parameter fluctuations with contact times and inlet chromate concentrations. Therefore, relying on fixed-parameter values can lead to faulty predictions and, therefore, to poor controllability of the chromate removal ion-exchange system. Thus, in this work, we evaluated the variation of parameters with respect to resin contact times and inlet chromate concentrations and performed a detailed sensitivity analysis and confidence region studies. This work improves the accuracy of the modified Thomas model fivefold and demonstrates its potential for use in process control decisions.

Excessive phosphorus in aquatic environments can lead to eutrophication, posing a significant deterioration of water quality. In this study, modified steel slag was used as a novel filter media in the biological aeration filter (BAF) to achieve a bioinduced phosphorus crystallization process for simultaneous removal and recovery of phosphorus from municipal wastewater. Phosphorus removal efficiency could reach 80% during 4 days of operation due to high adsorption capacity of the modified steel slag in the single BAF reactor, but the phosphorus removal efficiency decreased to 30% after 30 days of operation. The phosphorus removal efficiency of the BAF system increased to 70% under alternating anaerobic-aerobic (A/O) operation condition. Concentration of ${\mathrm{PO}}_4^{3-}\text{-}\mathrm{P}$ in anaerobic effluent reached $19.9\mathrm{mg}/\mathrm{L}$ at 68 days of operation and exceeded that in influent ($10.6\mathrm{mg}/\mathrm{L}$), indicating that phosphorus accumulating organisms (PAOs) were successfully enriched in the alternating A/O BAF system. Hydroxyapatite (HAP) crystals formation was confirmed based on analysis of scanning electron microscopy coupled with energy dispersive X-ray (SEM-EDX) and X-ray diffraction (XRD). The proposed phosphorus removal mechanism suggests that the release of phosphorus from PAOs and the release of ${\mathrm{Ca}}^{2+}$ and ${\mathrm{OH}}^{-}$ from the modified steel slag is beneficial to HAP crystals formation. These results indicated that the bioinduced phosphorus crystallization process achieved to improve phosphorus removal efficiency of the alternating A/O BAF system. This finding is a significant improvement to both biological and crystallization phosphorus removal processes, and has significant potential application for removal and recovery of phosphorus in wastewater treatment.

As the abundance and diversity of antibiotic resistance genes increases in the environment, there is a concurrent increase in the threat to public and ecosystem health. Extracellular antibiotic resistance genes (eARGs) are cell-free DNA that can promote the development of antibiotic resistance via transformation by competent bacterial cells. Despite this role, eARGs have not been well characterized in different environmental waters. Their small size and low concentrations in some aquatic environments render them difficult to extract. The aim of this research was to modify an eARG extraction method to determine the abundance of both eARGs and intracellular ARGs (iARGs) in the same water sample. The modified method, consisting of sequential filtration to separate iARGs from eARGs, adsorption-elution with aluminum hydroxide–coated silica gel, and precipitation, extracted eARGs and iARGs with a recovery rate between 79.5% and 99.0%. The novel method was then utilized for the extraction of the extracellular and intracellular fractions of four ARGs, one mobile genetic element, and the 16S rRNA in tap water, river surface water, lake surface water, stormwater, and wastewater effluent. This is the first instance in which the extracellular and intracellular fractions of the 16S rRNA, $intI1$, $bl{a}_{\mathrm{TEM}}$, $erm\mathrm{F}$, $sul1$, and $tet\mathrm{C}$ genes in stormwater and lake surface water are reported. In addition, this modified method enabled the quantification of the extracellular concentration of the erythromycin resistance gene $erm\mathrm{F}$ in environmental waters for the first time; the gene’s abundance ranged from $1.26\times {10}^5$ to $8.82\times {10}^6$ gene copies/L across the aquatic waters sampled. The extracellular abundance of the mobile genetic element $intI1$, moreover, was quantified in tap water ($7.00\times {10}^4$ gene copies/L) for the first time. The validation and application of this method to diverse environmental matrices should allow for further research to be conducted to better understand the role of eARGs in the spread of antibiotic resistance.

Regular water quality monitoring is required for protecting the physiochemical and bacteriological quality of surface water and to ensure water is meeting beneficial use criteria. This study investigated the effect of the time of sample collection on bacterial abundance and physicochemical parameters in an urban stream influenced by wastewater effluent but no rain events over 5 days on 3-h intervals. Temperature, discharge, pH, and conductivity were monitored onsite and they varied significantly ($P<0.05$) hourly. Total coliform and E. coli were measured in the stream water, sediments, and the treatment plant effluent. Over a day, microbial abundance varied eightfold to 21-fold upstream and twofold to 22-fold downstream of the discharge point for total coliform and E. coli, respectively. Compared with the regulatory 206 colony forming units (CFU)/100 mL coliform limit, stream samples exceeded safe limits in 70% of observations at 08:00, 50% at 11:00 and 14:00, and 10% at 17:00. Sediment samples from the upstream and downstream locations showed no significant variation in the microbial abundance based on time of sample collection, although the wastewater effluent effect was clearly seen. These results suggest repeated sampling of streams should be conducted at the same time of day to accurately inform risk-based sampling plans.