High-temperature technology survey and comparison among incineration, pyrolysis, and gasification systems for water resource recovery facilities.

Solids from wastewater treatment undergo processing to reduce mass, minimize pathogens, and condition the products for specific end uses. However, costs and contaminant concerns (e.g., per- and polyfluoroalkyl substances [PFAS]) challenge traditional landfill and land application practices. Incineration can overcome these issues but has become complicated due to evolving emissions regulations, and it suffers from poor public perception. These circumstances are driving the re-emergence of pyrolysis and gasification technologies. A survey of suppliers was conducted to document differences with technologies. Both offer advantages over incineration with tailored production of a carbon-rich solid, currently less stringent air emission requirements, and lower flue gas flows requiring treatment. However, incineration more simply combines drying and thermal processing into one reactor. Equipment costs provided favor pyrolysis and gasification at lower capacities but converge with incineration at higher capacities. Long-term operational experience will confirm technology competitiveness and elucidate whether pyrolysis and gasification warrant widespread adoption. PRACTITIONER POINTS: Pyrolysis and gasification systems are gaining traction in the wastewater industry with several full-scale installations operating, in construction, or design Several advantages, but some disadvantages, are considered in comparison with incineration Organic contaminants, including PFAS, will undergo transformation and potentially complete mineralization through each process.

Pyrolysis and gasification at water resource recovery facilities: Status of the industry.

Wastewater treatment generates solids requiring subsequent processing. Costs and contaminant concerns (e.g., per- and polyfluoroalkyl substances [PFAS]) are challenging widely used landfilling and land application practices. These circumstances are partly driving the re-emergence of pyrolysis and gasification technologies along with beneficial reuse prospects of the char solid residual. Previously, technologies experienced operational challenges leading to revised configurations, such as directly coupling a thermal oxidizer to the reactor to destroy tar forming compounds. This paper provides an overview of pyrolysis and gasification technologies, characteristics of the char product, air emission considerations, and potential fate of PFAS and other pollutants through the systems. Results from a survey of viable suppliers illustrate differences in commercially available options. Additional research is required to validate performance over the long-term operation and confirm contaminant fate, which will help determine whether resurging interest in pyrolysis and gasification warrants widespread adoption. PRACTITIONER POINTS: Pyrolysis and gasification systems are re-emerging in the wastewater industry. Direct coupling of thermal oxidizers and other modifications offered by contemporary systems aim to overcome past failures. Process conditions when coupled with a thermal oxidizer will likely destroy most organic contaminants, including PFAS, but requires additional research. Three full-scale facilities recently operated, several in construction or design that will provide operating experience for widespread technology adoption consideration.

Comparison of random forest and multiple linear regression to model the mass balance of biosolids from a complex biosolids management area.

The use of biosolids as a soil amendment provides an important alternative to disposal and can improve soil health; however, distribution for water resource recovery facilities (WRRFs) in the United States can be challenging due to decreasing cropland, increased precipitation, variable plant operations, and financial constraints. Although statistical modeling is commonly used in the water sector, machine learning is still an emerging tool and can provide insights to optimize operations. Random forest (RF), a machine learning model, and multiple linear regression (MLR) were used in this study to model the mass balance of biosolids from a complex biosolids management area. The RF model outperformed (R2 = 0.89) the MLR model (R2 = 0.49) and showed that rainfall was a major factor impacting distribution. Storage for dried biosolids would help decouple drying operations from wet weather and increase distribution. This study demonstrated how machine learning can assist in decision-making processes for long-term planning at WRRFs. PRACTITIONER POINTS: Random forest predicted the 7-day average mass balance of biosolids from a complex biosolids management area. Decoupling biosolids drying operations from wet weather was identified as the highest operational priority. Machine learning outperformed multiple linear regression and can be an important tool for the water sector.

Long-term biosolids planning with an operational mega reservoir for combined sewer overflow-impacted stormwater capture.

The Metropolitan Water Reclamation District of Greater Chicago adopted the Tunnel and Reservoir Plan (TARP) to reduce combined sewer overflow (CSO) events in the Chicago region. The Thornton Composite Reservoir (TCR) became operational in 2015 providing an additional 30 million m3 of CSO-impacted stormwater capacity. In the United States, no other mega reservoirs are in operation to provide as a reference to study the long-term impacts of biosolids operations in water resource recovery facilities. The mean daily volume pumped from the Calumet TARP system to the Calumet Plant increased 144-238 m3 from 2012-2014 to 273-360 m3 from 2016-2018. Overall annual digester feed solids for the 2016-2018 post-TCR period were 28,182 Mg, which was 11 percent less than the mean for the 2012-2014 period of 31,745 Mg. Annual digester draw solids for the 2016-2018 post-TCR period were 19,422 Mg, which were 4 percent less than the 2012-2014 pre-TCR period mean of 20,190 Mg. This paper demonstrated a decrease in digester feed loading to the Calumet Plant and, ultimately, a decrease in digester draw solids with an overall increase in plant and TARP flow in the years following operation of the TCR for the capture and treatment of CSO-impacted stormwater. PRACTITIONER POINTS: Reservoirs capturing combined sewer overflow-impacted stormwater improve water quality of local waterways. Mega reservoirs may impact solids loading to water resource recovery facilities. Hydraulic loading to water resource recovery facilities may be substantial with mega reservoirs.

Prediction of odor complaints at a large composite reservoir in a highly urbanized area: A machine learning approach.

Odorous compound emissions and odor complaints from the public are rising concerns for agricultural, industrial, and water resource recovery facilities (WRRFs) near urban areas. Many facilities are deploying sensors that measure malodorous compounds and other factors related to odor creation and dispersion. Focusing on the Metropolitan Water Reclamation District of Greater Chicago's (MWRDGCs) Thornton Composite Reservoir (7.9 billion gallon capacity), we used meteorological, operational, and H2S sensor data to train a 3-day advance-warning predictor of local odor complaints, so as to implement targeted odor prevention measures. Using a machine learning approach, we bypassed difficulties in modeling both physical dispersion and human perception of odors. Utilizing random forest algorithms with varied settings and input attributes, we find that a small network of H2S sensors, meteorological data, and operational data are able to predict odor complaints three days in advance with greater than 60% accuracy and less than 25% false-positive rates, exceeding MWRDGC's standards required for full-scale deployment. PRACTITIONER POINTS: A random forest algorithm trained on H2 S, weather, and operations data successfully predicted odor complaints surrounding a large composite reservoir. Thirty-two data attribute combinations were tested. It was found that H2 S sensor data alone are insufficient for predicting odor complaints. The best predictor was a Random Forest Classifier trained on weather, operational, and H2 S readings from the reservoir corner locations. This study demonstrates odor complaint prediction capability utilizing a limited set of data sources and open-source machine learning techniques. Given a small network of H2 S sensors and organized data management, WRRFs and similar facilities can conduct advance-warning odor complaint prediction.

A reduction in triclosan and triclocarban in water resource recovery facilities' influent, effluent, and biosolids following the U.S. Food and Drug Administration's 2013 proposed rulemaking on antibacterial products.

Pharmaceutical and personal care product compounds (PPCPs) comprise a large and diverse group of chemical compounds, including prescription and over-the-counter drugs and cleaning agents. Although PPCPs in the effluent and biosolids of water resource recovery facilities (WRRFs) are currently not regulated, public interest has led the Metropolitan Water Reclamation District of Greater Chicago to monitor for 11 PPCPs in the influent, effluent, and biosolids at its seven WRRFs. In 2016, the U.S. Food and Drug Administration (FDA) issued a final rule establishing that 19 specific ingredients, including triclosan and triclocarban, were no longer generally recognized as safe and effective, which prohibits companies from marketing soaps as antibacterial if they contain one or more of these ingredients. It was presumed that since the proposed rulemaking in 2013, manufacturers began to remove these active ingredients from their products. Annual monitoring of 11 PPCPs from 2012 to 2017 demonstrated a 71% decrease in triclosan and 72% decrease in triclocarban in per capita influent loading into seven WRRFs. There was a 70% decrease in triclosan and 80% decrease in triclocarban concentrations in biosolids. These declines suggest the FDA rule for the reduction in use of these compounds was effective and resulted in manufacturers removing these ingredients from their products. PRACTITIONER POINTS: Reduction in triclosan and triclocarban per capita influent loading observed from 2012 to 2017. Reduction in triclosan and triclocarban biosolids loading observed from 2012 to 2017. 2016 FDA rulemaking on antimicrobial soaps was effective in removing triclosan and triclocarban from these products. Positive impact on quality of biosolids land applied to farmland.

Greening a Steel Mill Slag Brownfield with Biosolids and Sediments: A Case Study.

The former US Steel Corporation's South Works site in Chicago, IL, is a 230-ha bare brownfield consisting of steel mill slag fill materials that will need to be reclaimed to support and sustain vegetation. We conducted a case study to evaluate the suitability of biosolids and dredged sediments for capping the steel mill slag to establish good quality turfgrass vegetation. Eight study plots were established on a 0.4-ha parcel that received biosolids and dredged sediment blends of 0, 25, 50, or 100% biosolids (v/v). Turfgrass was successfully established and was thicker and greener in biosolids-amended sediments than in unamended sediments. Concentrations of N, P, K, and micronutrients in turfgrass tissues increased with increasing biosolids. Soil organic carbon, N, P, and micronutrients increased with increasing biosolids. Cadmium, Cu, Ni, and Zn concentrations in biosolids-amended sediments also increased with increasing biosolids but were far below phytotoxicity limits for turfgrass. Lead and Cr concentrations in biosolids-amended plots were comparable to concentrations in unamended sediments. Groundwater monitoring lysimeters and wells below the study site and near Lake Michigan were not affected by nutrients leaching from the amendments. Overall, the results from this case study demonstrated that blends of biosolids and dredged sediments could be successfully used for capping steel mill slag brownfield sites to establish good quality turfgrass vegetation.

Hexavalent chromium reduction by tartaric acid and isopropyl alcohol in Mid-Atlantic soils and the role of Mn(III,IV)(hydr)oxides.

Chromium is a naturally occurring transition metal and a soil contaminant in the Cr(VI) oxidation state, but reduction of Cr(VI) to Cr(III) mitigates its toxicity. Tartaric acid reduces Cr(VI) via a termolecular complex with isopropyl alcohol and Cr(VI), but its efficacy in soils has not been demonstrated. Five Mid-Atlantic soils from Maryland, U.S. were examined for their potential to enhance the reduction of Cr(VI). A control treatment (no soil +12 mM tartaric acid + 0.29 M isopropyl alcohol) reduced 0.37 mM Cr(VI) (19%) in 99 h. Reduction was enhanced to 1.97 mM (99%) with addition of a Russett Ap soil horizon (fine-loamy, mixed, semiactive, mesic Typic Hapludult). With a half-life of 18.7 h, the rate of reduction of Cr(VI) with the Russett soil sample was 20 times faster than with no soil (371 h). Soil Mn was solubilized in this reaction and plays a role in the enhanced reduction of Cr(VI). Mn(III/IV)(hydr)oxide-coated quartz sand reduced 1.24 mM (62%) Cr(VI), with all of the Mn(III,IV)(hydr)oxides solubilized. The addition of isopropyl alcohol and tartaric acid to soils enhances the reduction of Cr(VI), and this reduction is further enhanced by the catalytic behavior of Mn(II) from easily reducible Mn(III,IV)(hydr)oxides in soil.

Hexavalent chromium reduction in solution and in chromite ore processing residue-enriched soil by tartaric Acid with isopropyl alcohol and divalent manganese as co-reductants.

Chromite ore processing residue (COPR), the solid waste product from the high-temperature alkaline processing of ferrochromite (FeO·CrO), contains Cr(VI) in soluble and insoluble compounds formed in the roasting process. This research investigated tartaric acid in combination with Mn and isopropyl alcohol (IPOH ) as co-reductants for reagent- and COPR-derived Cr(VI). The reduction of Cr(VI) by tartaric acid alone at pH 5.0 or greater was negligible; however, in the presence of Mn or IPOH, reduction occurred in hours. Isopropyl alcohol enhanced Cr(VI) reduction, probably via formation of a termolecular complex with the alcohol, tartaric acid, and Cr(VI). In aqueous solutions of reagent-derived Cr(VI) at pH 4, 12 mmol L tartaric acid with 1.0 mmol L Mn or 1.0 mmol L Mn and 0.29 mol L (2% v/v) IPOH reduced 1.0 mmol L Cr(VI) in 48 h. The same treatments at pH 5.5 reduced 0.60 and 0.58 mmol L Cr(VI) (60%) in 96 h, respectively. A minimum half-life of 10.2 h was calculated from first-order rate constants obtained from Mn and IPOH-Mn co-reductant treatments with tartaric acid at pH 4. The most COPR-derived Cr(VI) reduced in suspension was by IPOH and Mn at high acidity (pH 5.8), which reduced 0.52 mmol L (52%) of the COPR-derived soluble Cr(VI) at 96 h. The enhanced reduction of soluble Cr(VI) by tartaric acid by the addition of Mn proceeds within a complex formed by an esterification reaction between tartaric acid and Cr(VI) with Mn bound to tartaric acid. The combined treatment of tartaric acid, IPOH, Mn, and a strong acid to lower the pH of COPR-enriched soils would be effective in field applications of this chemistry. By creating a slurry of the field soil with these amendments, mass transfer limitations would be overcome, and Cr(VI) would be reduced to Cr(III) in days.

Oxidation-reduction transformations of chromium in aerobic soils and the role of electron-shuttling quinones.

Oxidation of Cr(III) and reduction of Cr(VI) can occur simultaneously in aerobic soils, but the mechanisms involved are not well-understood, especially how electron shuttling by redox-active organic acids is involved. A and B soil horizons from three topohydrosequences from the Coastal Plain and Piedmont physiographic provinces of Maryland were chosen to investigate oxidation-reduction transformations of Cr under field moist conditions. Reduction of added Cr(VI) to Cr(III) was observed in all 18 samples, and 11 demonstrated enhanced reduction with added anthraquinone-2,6-disulfonate (AQDS) acting as an electron shuttle in 24 h quick tests under aerobic conditions. Oxidation of Cr(III) to Cr(VI) was observed in 12 samples, with 7 demonstrating diminished oxidation with AQDS added. Cr(VI) was undetectable after 11 d of incubation when lactic acid was added as a reductant for Cr(VI) to the Watchung soil A horizon. This reduction occurred in the presence of AQDS and a high salt background to suppress microbial growth, suggesting abiotic reduction was the dominant pathway. The results of this study demonstrate that in field-moist, aerobic soils, the electron shuttle, AQDS, enhanced Cr(VI) reduction and inhibited Cr(III) oxidation. This suggests redox-active organic C amendments and electron shuttles can be important in enhancing rates and extent of Cr(VI) reduction, while inhibiting Cr(III) oxidation in the in situ remediation of Cr(VI)-contaminated soils.