Journal of Environmental Engineering

Stack emissions have increased the carbon footprint by devastating impacts on human lives and vegetation as well as reducing the ozone layer to amplify the possibility of global warming. So the extent of emitted gases in the atmosphere or on the ground and possible conversion pathways of gases are of interest to understand the advection, diffusion and dispersion patterns, acid rain precursor formation, ozone layer depletor generation, and scopes of air pollution regulation development. A number of factors such as atmospheric stability conditions, wind velocity, stack height, downwind distance from the stack, vertical distance from ground level, and ambient temperature of the surrounding environment of the plume were studied to depict the advection, diffusion, and dispersion pattern of gases and particles in the atmosphere. The plume could travel downwind distances of 10.5 and 1,720 km in stability conditions A and D, respectively, for high mass emission (HME), although wind velocity and stack height had significant impacts on dispersion and deposition pattern. Ambient temperature, turbulence, and density gradient could similarly play important roles in mixing and the ultimate fate and transport of plume elements. The magnitude of vertical dispersion of the plume might influence the formation of acid rain precursors and depletion of the ozone layer in the troposphere and stratosphere. Ozone layer stability depends not only on atmospheric chlorine and nitrogen elements but also on increasing temperature due to the presence of heat-trapping elements where about 0.0011%/day and 0.00035%/day of the ozone layer may change at $-25°\mathrm{C}$ and $-50°\mathrm{C}$ in the atmosphere, respectively. Currently available scientific literature has not discussed the influence of all these factors on the advection and dispersion of pollutants and ozone depletion by heat-trapping elements.

Four chloraminated drinking water distribution systems (CDWDSs) required to maintain numeric versus “detectable” residuals were spatially and temporally sampled for water quality and associated trihalomethane (THM) and haloacetic acid (HAA) formation. Monochloramine decreased from entry point (EP) to maximum residence time (MRT) samples while THMs and HAAs initially increased and then stabilized or slightly decreased. Subsequently, EP and MRT samples were used in laboratory-held studies to further evaluate disinfectant residual stability, chloramine speciation, and nitrification occurrence. MRT water exhibited a faster monochloramine concentration decline compared to EP water, indicating a decreasing disinfectant residual stability from increasing water age through distribution. Using a simple technique based on published inorganic chloramine chemistry, samples were also investigated for nondisinfectant positive interference (NDPI) on total chlorine measurements. NDPI concentrations represented up to 100% of the total chlorine concentration when total chlorine concentrations decreased to $0.05{\mathrm{mg}\text{-}\mathrm{Cl}}_2/\mathrm{L}$, indicating little to no effective disinfectant residual remained.

Enhanced biological phosphorus removal (EBPR) is a growing, succeeding, and recognized process for removing phosphorus biologically from wastewater. Four sequencing batch reactor (SBR) plants with capacities of 120, 87.5, 50, and 3 million L per day (MLD) from different Indian locations were analyzed for EBPR. The 120 MLD Varanasi, 87.5 MLD Mumbai, and 50 MLD Gurgaon plants were working effectively for EBPR; $>75\%$ total phosphorus (TP) removal was observed at milligrams of readily biodegradable chemical oxygen demand (rbCOD) per milligram ${\mathrm{TP}}_{\mathrm{removed}}$ of 12.0, 14.4, and 18.6, respectively; however, the 3 MLD Roorkee SBR was working mainly as adequate nitrogen removing technology at milligrams rbCOD/mg ${\mathrm{TP}}_{\mathrm{removed}}<8$. The linear increasing trend was observed between rbCOD/COD (%) and EBPR (%) at $R^2=0.99$ ($p<0.05$ and $r=0.99$) in plants. Optical microscopic examinations were performed to identify the intracellular polymers [poly-β-hydroxybutyrate (PHB) and polyphosphates] in the EBPR sludge. This study focuses on optimizing the SBR designs (selector and non-selector based) for EBPR and identifying the relationships between wastewater characteristics and phosphorus removal governed by typical microbial functions with the perspective of optimizing decentralized treatment systems of India.

Abstract

Pressure sewer networks offer a flexible alternative to more traditional gravity-based systems for the conveyance of wastewater. Some of the issues associated with pressure sewer networks (e.g., odor, septicity) arise from inappropriate design assumptions. Daily inflow volumes are a crucial part of the design of pressure sewer systems; gravity design parameters are presently used to design pressure sewer networks in New Zealand. This study analyzed flow data from six representative pressure sewer networks (approximately 24% of operating pump units in New Zealand) to identify the daily inflow volumes per connected pump unit. The results indicated that the median inflow volume was approximately $410\mathrm{L}/\mathrm{pump}\mathrm{unit}/\mathrm{day}$. This inflow is much lower than current council design standard assumptions, which range from 650 to $\mathrm{1,000}\mathrm{L}/\mathrm{pump}\mathrm{unit}/\mathrm{day}$. Pressure sewer network designs using higher daily loading rates may result in oversized networks that are detrimental to the network’s operation and performance, especially for meeting minimum self-cleansing velocities and wastewater retention times. The data collection period included the first COVID-19 lockdown in New Zealand. Four lockdown levels were introduced, with Level 4 and Level 3 being the most restrictive and requiring all but essential workers to stay and work from home. Levels 1 and 2 allowed people to return to their place of work. The data indicated that the Level 4 lockdown period caused a 25% increase in daily inflow volumes. In comparison, the Level 3 and 2 lockdown periods increased the daily inflow volumes by 20% and 15%, respectively. The analysis also included the networks’ wet-weather responses. Minor rain events did not significantly affect the daily inflow volumes. However, gravity networks that have been retrofitted with pressure sewer networks may be more subject to aging or damaged laterals and illegal stormwater connections, both of which are likely to result in a more significant wet-weather response. The paper also discusses the issues associated with an overreliance on standardized design methods without understanding their proper application and the pitfalls of adopting gravity sewer design assumptions for pressure sewer network designs. The findings of this paper will further allow determination of the sensitivity of network design outcomes, performance, and maintenance requirements to the design methods and assumptions for pressure sewer networks, not only in New Zealand but in any country that uses the technology.

Practical Applications

Experience from within the engineering industry suggests that some asset owners may not have a clear understanding of aspects of pressure sewer technology or its appropriate operational philosophy. Another factor may be that because of a lack of data and experience with the technology, some asset owners may be unsure how pressure sewer networks should be incorporated into existing gravity networks. Asset owners and residential developers are facing both challenges and opportunities for wastewater management; however, the role of alternative technologies to address this is unclear. Furthermore, there is a greater focus on sustainability within the construction industry, and asset owners are encouraged to continually seek ways to minimize the impact of their activities on the environment by setting carbon reduction targets and reducing energy consumption. It is important that pressure sewer network designers consider the effects of lower design inflow volumes when assessing a pressure sewer network’s performance, and to understand the implications or potential issues with oversized networks.

In this study, the effect of hydrothermal treatment (HTT) and the evaluation of its application as a pretreatment (HTP) and inter-treatment (HIT) on anaerobic digestion (AD) and fermentation of thickened waste activated sludge (TWAS) were examined. Two configurations were tested: (1) hydrothermal pretreatment, where the hydrothermal treatment was applied prior to single and two-stage anaerobic digestion; and (2) hydrothermal inter-treatment, where the hydrothermal treatment was applied after the first stage, fermentation, and prior to the second stage, methanogenesis. The results revealed the positive impact of hydrothermal pretreatment in both fermentation and anaerobic digestion processes. The chemical oxygen demand (COD) solubilization was higher through HTP (25.5%) than HIT (13%). Hydrothermal pretreatment increased the volatile fatty acids (VFA) production by 40% compared to the raw sample. The results also revealed no significant differences in the methane yield when hydrothermal treatment was applied as pretreatment or inter-treatment. The methane yield for the hydrothermal pretreatment and hydrothermal inter-treatment scenarios were $230{\mathrm{mLCH}}_4/{\mathrm{gTCOD}}_{\mathrm{added}}$ and $227{\mathrm{mLCH}}_4/{\mathrm{gTCOD}}_{\mathrm{added}}$, respectively, compared to $158{\mathrm{mLCH}}_4/{\mathrm{gTCOD}}_{\mathrm{added}}$ for the raw sample.

Abstract

In wastewater treatment design, it is common practice to test aeration equipment in clean water first, and then extrapolate the result to wastewater via a correction factor. In addition to the many variables, such as the organic loading and physicochemical properties of the water, that affect its magnitude, there is evidence that biochemical reactions play an important role in oxygen transfer in wastewater. The proposed model for in-process oxygen transfer is based on the novel concept of a resistance to gas transfer due to the microbial activity in the field. The hypothesis proposed in this study is that the alpha factor $\alpha$, or the relative mass transfer coefficient, which is the ratio of the mass transfer coefficient in wastewater $K_L{a}_f$ to the mass transfer coefficient in water $K_{L}a$, is independent of microbial activities in an aeration basin, and the corresponding performance ratio in terms of efficiencies is the same function as $\alpha ={\mathrm{OTE}}_f/\mathrm{OTE}$, where subscript $f$ denotes field water characteristics. The common approach is to report the ${\mathrm{OTE}}_f$ from off-gas measurements in the field and translate this value to $K_L{a}_f$, giving $\alpha$ as the ratio ${\mathrm{OTE}}_{\mathrm{pw}}/\mathrm{OTE}$ that gives only a false or apparent alpha, where the subscript pw denotes process water undergoing biological stabilization due to microbial metabolism. The field-determined ${\mathrm{OTE}}_{\mathrm{pw}}$ is affected by the respiration rate $R$, which is dictated by the microbial activity, which is mathematically associative to the transfer process by addition and not associative by multiplication with a scalar quantity. A gas-phase mass balance for oxygen around a completely mixed aeration tank confirmed the association nature of the alpha factor. Examination of test data extracted from the literature indicates that the field-determined ${\mathrm{OTE}}_{\mathrm{pw}}$ is indeed affected by the respiration rate $R$. Using the data collected from previous investigators, the alpha factor has a consistent magnitude of about 0.8 for domestic sewage.

Practical Applications

The activated sludge (AS) process is an important wastewater treatment technology that requires aeration, which is an energy-intensive process. Estimating the oxygen transfer rates under various process conditions is crucial for design and operation of aeration systems. Because clean-water testing is an established method to determine the aeration performance of diffusers, it is common practice to extrapolate the result to wastewater via a correction factor, $\alpha$. In addition to the many variables that affect its magnitude, there is evidence that biochemical reactions play an important role in oxygen transfer in wastewater. A proposed model based on the novel concept of a resistance to gas transfer due to the microbial activities in the aeration basin showed that the correction factor is quite independent of these activities. Treating $\alpha$ as pertaining only to the wastewater characteristics will provide some control over its parameter estimation, which is needed for any sensible design of a biological treatment plant. Currently, mechanistic models continue to evolve in scope and sophistication to cover all aspects of design and operational optimization, with the support of various sensors for water resource recovery facilities (WRRFs). The findings of this study may be utilized in the development of optimization strategies for energy consumption in such facilities.

The effect of FeS on reactive brilliant red X-3B (RBRX3) removal performance and on the microbial community was investigated in a homemade constructed wetland–microbial fuel cell (CW-MFC) coupled system. Under the test conditions (RBRX3 $\mathrm{concentration}=100\mathrm{mg}/\mathrm{L}$; influent glucose concentration ranged from 0 to $300\mathrm{mg}/\mathrm{L}$), the decolorization rate of RBRX3 and the chemical oxygen demand (COD) in the FeS group were 95.14%–98.86% and 30.53%–86.65%, respectively; these figures were 13.83%–55.52% and 2.57%–19.9% higher, respectively, than those of the gravel group. The output voltage and maximum power density of the FeS group increased by $0.098–0.101\mathrm{V}$ and $0.078–0.420\mathrm{W}/{\mathrm{m}}^3$, respectively, compared to the gravel group. The differences between the two groups mainly occurred in the bottom and anode regions; the FeS filling in these regions played an important role. FeS had an obvious effect on the microbial community structure; Firmicutes and Clostridium in the bottom and anode regions became the dominant species. The conversion of iron and sulfur in FeS between different valence states was achieved under the synergistic action of microorganisms such as iron-reducing bacteria (IRB), sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB), which promoted electron transfer and improved the decolorization and degradation effect of azo dyes and the system’s electricity production performance. FeS added to the CW-MFC system can provide electrons for azo dye wastewater treatment, thereby reducing the addition of organic carbon sources.

A novel hybrid fed-batch moving-bed bioreactor (MBBR) system was developed for the treatment of refinery wastewater containing a wide range of phenol ($250–\mathrm{1,000}\mathrm{mg}/\mathrm{L}$) and ammonia-nitrogen ($50\mathrm{mg}/\mathrm{L}$) using an indigenous mixed microbial culture. A hybrid system containing a native mixed microbial consortium and comprising three MBBR units connected in series and operating with a 24-day hydraulic retention time (HRT) and a recycle ratio of 1.0 was evaluated under three environmental conditions. MBBR units in the system were operated in anaerobic, anoxic, and aerobic conditions in fed-batch mode. The hybrid system proficiently removed the phenol (99%), ammonia-nitrogen (95%), and reduced chemical oxygen demand (COD) (98%) from maximum feed concentrations of 1,000, 50, and $\mathrm{3,077}\pm 6\mathrm{mg}/\mathrm{L}$, respectively. The overall ${\mathrm{NH}}_4\text{-}\mathrm{N}$ removal efficiency of the system decreased by 4.7%, and COD reduction efficiency increased by 2% while varying the feed phenol concentration from 250 to $\mathrm{1,000}\mathrm{mg}/\mathrm{L}$. However, the removal rate for phenol (20.72 to $82.42\mathrm{mg}/\mathrm{L}·\mathrm{day}$) and ${\mathrm{NO}}_3\text{-}\mathrm{N}$ (10.57 to $17.81\mathrm{mg}/\mathrm{L}·\mathrm{day}$) increased in the anaerobic and anoxic reactor, respectively. The ammonia removal rate for the aerobic reactor decreased from 8.14 to $7.377\mathrm{mg}/\mathrm{L}·\mathrm{day}$. Ultraviolet (UV)-visible spectroscopy and gas chromatography-mass spectroscopy (GC-MS) were used to identify the formation of intermediates (catechol and muconic acid) during the biotransformation of phenol. Scanning electron microscopy (SEM) analysis showed better adhesion of the mixed microbial community in the pores of the carrier media. The best fit of the modified Stover-Kincannon model confirmed that phenol and ${\mathrm{NH}}_4\text{-}\mathrm{N}$ utilization is a function of organic loading rate under steady-state conditions. The results of this investigation suggest that the newly developed hybrid system with indigenous mixed microbes can treat the heterogeneous pollutants discharged in refinery wastewater.

The performance of a modified upflow anaerobic sludge blanket (MUASB) reactor with a modified three-phase separator and a rope matrix, combined with SGBR in series was analyzed for the treatment of synthetic wastewater. The performance of the reactor series in terms of chemical oxygen demand (COD) removal was evaluated by varying the operational hydraulic retention times (HRT) from 12 to 30 h. The optimum HRT for the reactor series was found to be 24 h, with a corresponding organic loading rate (OLR) of $8\mathrm{kg}\mathrm{COD}/{\mathrm{m}}^3/\mathrm{day}$. The maximum overall COD removal of the reactor series of 98.75% $\pm 0.62\%$ was obtained with the corresponding overall biogas production of $0.339\%\pm 0.01{\mathrm{m}}^3/\mathrm{kg}{\mathrm{COD}}_{\mathrm{digested}}$. The reactor series was found to be stable during the operational period in terms of volatile fatty acids (VFAs)/alkalinity ratio. The analytical hierarchy process was used for choosing a better treatment option among the alternatives based on the selected criteria. MUASB–static granular bed reactor (SGBR) series was found to be superior to the MUASB and the SGBR individually based on COD removal. The payback period for the reactor series was calculated to be 8 years (approximately). The MUASB-SGBR series was found to be robust, stable, and economical, with better performance in terms of COD removal.

In this study, a noteworthy increase in biogas generation from pine litter was achieved by codigesting it with food waste. Within the microbial communities present, a high level of species richness as well as diversity was observed among bacterial decomposers. Bacteroides dominated the population at 32.9%, with phylum Proteobacteria being the second at 27.4%. Further, bacteria belonging to the family Comamonadaceae, whose niche as lignin degraders has recently been acknowledged, were present. The sample additionally appeared enriched with acetogens, syntrophic acetogens, and methanogens, indicating probable replacement of communities with metabolic capabilities adapted to the particular stage of decomposition. Anaerobic digestibility of the process was also studied with the help of one kinetic and three mathematical models. Technoeconomic and sensitivity analysis of the process showed the process was feasible. The process will seek the attention of stakeholders and policymakers due to profitability while transferring the technology from lab to the pilot scale.

Ca–Al-layered double hydroxide (Ca/Al-LDH) is an excellent sorbent for wastewater decontamination and is widely used in the treatment of this phosphate and fluoride-containing wastewater. In this study, we propose a strategy using the wastes generated from treating high-concentration phosphate wastewater process to treat fluoride wastewater to maximize the value of LDH. The effects of environmental parameters such as reaction time, initial fluoride and phosphate concentrations, adsorbent concentration, and pH were investigated. The experimental results showed that when the initial ${\mathrm{F}}^{\text{-}}$ concentration was ${10\mathrm{mg}\hspace{0.17em}\mathrm{L}}^{-1}$, the removal rates of ${\mathrm{F}}^{\text{-}}$ were over 90%. To further understand the adsorption mechanism of ${\mathrm{F}}^{\text{-}}$ on solid waste, we employed characterization methods such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR), which were also able to characterize the adsorption products before and after the reaction. It was found that hydroxyapatite was formed after the removal of phosphate, while fluorapatite was formed at the F-substituted hydroxyl position after the removal of fluorine. The adsorption process of fluorine removal is a spontaneous endothermic adsorption process. This study shows that Ca/Al-LDH can be a promising material with a high development value, and the new strategy of sequentially removing phosphorus and fluorine using this material can maximize the value of this adsorbent.