Sludge Streams Research Articles

Electrochemical Cell Design and Operation for Copper Recovery from Chemical Mechanical Polishing Slurries

Copper (Cu) removal from chemical mechanical polishing (CMP) waste is critical to maintaining discharge compliance with local municipalities and the Environmental Protection Agency (EPA). Typical treatment of this waste stream has followed two conventions: either coagulant-based precipitation or ion exchange (IX).1 Many industries use iron-based coagulants for metal removal from wastewater to meet discharge compliance. However, the process is often cumbersome, requires long settling times and significant chemical utilization, and results in a sludge stream that must be shipped and disposed of properly, eliminating the possibility for metal recovery. Since the concentrations for Cu removal from CMP waste streams is normally low (<100 ppm), IX has generally been the preferred treatment method. Nevertheless, IX also has some negatives associated with the process. Hydrogen peroxide can and will damage the IX media, resulting in premature replacement. The industry has dealt with this impact by employing one-time use media, but this adjustment means that media is only used once before being shipped offsite for regeneration. This results in operational impacts due to the need for oversight of media replacement and also eliminates the ability for Cu to be recovered at the originating process site.In this talk, electrochemical methods to recover Cu from CMP wastewaters will be described. Electrochemical cell design and operation will be shown to provide Cu removal across wide ranges of concentration, and the depth of Cu separation (<2 ppm) and efficiency of the process will be discussed. The presence of hydrogen peroxide and its influence on the process will be evaluated. The removal and recovery of Cu will be shown in a complete cycle, demonstrating the ability to recover and reuse Cu directly at a process site. The impact of (1) pH, (2) chelator type, and (3) abrasive (SiO2) will also all be reviewed. Changes to the slurry, as analyzed pre- and post-electrochemical separation, will be characterized to determine possibilities for the reuse of the CMP slurry itself. Ultimately, the ability to design process systems using electrical input and minimal chemical additives to treat wastewater to municipal and EPA specifications while maximizing recycling efforts will be evaluated and presented.

Innovative approach for predicting biogas production from large-scale anaerobic digester using long-short term memory (LSTM) coupled with genetic algorithm (GA)

An artificial neural network (ANN) model called long-short term memory (LSTM), coupled with a genetic algorithm (GA) for feature selection, was used to predict biogas production of large-scale anaerobic digesters (ADs) of Tehran South Wastewater Treatment Plant (Iran), with a biogas production of approximately 30,000 Nm3/d. In order to employ the real conditions, the hydraulic retention time (HRT) of the ADs (21 days) was considered as the LSTM look-back window. To evaluate the model predictions, three different scenarios were defined. In the first scenario, the model predicted the produced biogas by using raw wastewater characteristics and reached the coefficient of determination of R2 = 0.84. The GA selected four out of eleven parameters of raw wastewater, including loads of BOD5, COD, TSS, and TN (kg/d), as the most informative data for the model. In the second scenario, the model predicted the produced biogas by employing the data of the thickened sludge streams entering the ADs and yielded a higher accuracy (R2 = 0.89). In this scenario, GA selected two out of six parameters of the sludge streams, including total flow rate (m3/d) and average solids content (w/w%). Finally, in the third scenario, by putting the parameters of the two previous scenarios together, the model's prediction accuracy increased slightly (R2 = 0.90). The results demonstrated that the GA-LSTM modeling technique could achieve reliable performance in predicting biogas production of large-scale ADs by including HRT in modeling procedure. It was also found that the raw wastewater characteristics severely affect AD behavior and can be successfully used as the input data of the AD models.

Impact of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) on secondary sludge microorganisms: removal, potential toxicity, and their implications on existing wastewater treatment regulations in Canada.

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) are two of the most commonly researched per- and polyfluoroalkyl substances (PFAS). Globally, many long-chain PFAS compounds including PFOS and PFOA are highly regulated and, in some countries, PFAS use in commercial products is strictly prohibited. Despite the legal regulation of these 'forever chemicals' under the Canadian Environmental Protection Act, PFOA and PFOS compounds are still found in high concentrations in discharges from wastewater treatment plants, both from liquid and sludge streams. Yet, their potential impact on wastewater treatment effectiveness remains poorly understood. The findings of this research show that: (1) PFOS and PFOA might be hindering the overall outcome treatment performance - calling into question the efficacy of Canada's existing wastewater treatment regulatory standard (Wastewater Systems Effluent Regulations, SOR/2012-139), and (2) specific microorganisms from the Thiobacillus and Pseudomonas genera seem capable of adsorbing PFOS and PFOA onto their cell wall and even degrading the chemicals, but it is unclear as to what extent degradation occurs. The results also raise questions whether existing wastewater regulations should be expanded to include the detection and monitoring of PFAS, as well as the establishment of a regulatory wastewater treatment plant discharge standard for PFAS that is protective of human and ecological health.

Effective multipurpose sewage sludge and food waste reduction strategies: A focus on recent advances and future perspectives

Energy crisis and increasing rigorous management standards pose significant challenges for solid waste management worldwide. Several emerging diseases such as COVID-19 aggravated the already complex solid waste management crisis, especially sewage sludge and food waste streams, because of the increasingly large production year by year. As mature waste disposal technologies, landfills, incineration, composting, and some other methods are widespread for solid wastes management. This paper reviews recent advances in key sewage sludge disposal technologies. These include incineration, anaerobic digestion, and valuable products oriented-conversion. Food waste disposal technologies comprised of thermal treatment, fermentation, value-added product conversion, and composting have also been described. The hot topic and dominant research foci of each area are summarized, simultaneously compared with conventional technologies in terms of organic matter degradation or conversion performance, energy generation, and renewable resources production. Future perspectives of each technology that include issues not well understood and predicted challenges are discussed with a positive effect on the full-scale implementation of the discussed disposal methods.

Long term experiences in a pilot-scale high-rate activated sludge system with lamella clarifier: Effluent quality and carbon capture

The limited available area for treatment plants in population-dense settlements increases the need for technologies with smaller footprints. The high-rate activated sludge (HRAS) process aims to capture carbon from wastewater by limiting biological assimilation with a high loading rate which enables occupying a smaller footprint. The footprint of the HRAS system can be further reduced by using lamella clarifiers instead of conventional ones. Conventional clarifiers were used in previous studies on the operational parameters of the HRAS system. This study aims to determine the optimum operational conditions in terms of hydraulic retention time (HRT) (75 and 50 min) and dissolved oxygen (DO) concentration (0.2, 0.5, and 0.8 mg/L) of a HRAS system including a lamella clarifier using 124 days data. The best effluent quality and carbon capture were observed at HRT of 75 min and DO concentration of 0.5 mg/L, which was considered the optimum condition with the highest extracellular polymeric substances (EPS) production in the reactor. The high EPS production helped flocs come together and settle faster with the highest carbon capture compared to other operational conditions. Based on the mass balance, 41.7 % of chemical oxygen demand (COD), 34 % of total nitrogen (TN), and 60 % of total phosphorus (TP) in the influent were captured into the sludge stream at the optimum condition. Lower HRT and DO concentration decreased EPS production and led to particulate COD loss through effluent and hampered carbon capture. Furthermore, higher DO concentration caused more carbon loss through oxidation.

Radioactive waste immobilization of Hanford sludge in magnesium potassium phosphate ceramic forms

This paper evaluates immobilization of Hanford K-Basin tank sludge in magnesium potassium phosphate ceramic forms. The waste forms were produced using two simulated non-radioactive sludge streams, each with distinct characteristics and composition. Ceramicrete with wollastonite as filler was used as the matrix for this purpose. The resulting waste forms were tested for their mechanical properties, radiation stability, and leaching resistance. In another series of tests, the samples were vitrified in borosilicate glass and glass waste forms were produced. The Product Consistency Test, the American Nuclear Society's ANS 16.1 test, and the Toxicity Characteristic Leaching Procedure, which are used to develop waste acceptance criteria in the United States for permanent storage of treated waste, were used for evaluation of the leaching resistance of all waste forms.

Occurrence and Fate of Ultrashort-Chain and Other Per- and Polyfluoroalkyl Substances (PFAS) in Wastewater Treatment Plants

To better understand the fate of per- and polyfluoroalkyl substances (PFAS) during conventional and advanced wastewater treatment, 42 PFAS (C3–C14 perfluorocarboxylic acids (PFCAs), C3–C10 perfluorosulfonic acids (PFSAs), per- and polyfluoroethers, and perfluoroalkyl acid (PFAA) precursors) were investigated through the treatment trains at two municipal wastewater treatment plants (WWTPs) using a targeted analysis, the total oxidizable precursor (TOP) assay, and the estimation of partitioning to sludge. Short-chain (C3–C7) PFAAs were found in higher concentrations in wastewater samples, while long-chain (≥C8) PFAAs dominated in sludge samples. PFAA concentrations were elevated by the wastewater treatment processes, particularly after biological treatment (191.3 and 185.1% increases of PFAAs at WWTP-A and B). After TOP oxidation, PFCAs, particularly short-chain ones, increased considerably (up to 311.4 and 409.3% increases of PFCAs at WWTP-A and B). The study results indicated that the transformation of precursors into shorter chain PFAAs by biological treatment and the partitioning of longer chain PFAS into sludge streams are key factors determining the fate of PFAS in WWTPs. With the increasing impact of short-chain PFAS over time, future research should focus on the evaluation of the fate and distribution of historical and emerging PFAS in WWTPs.

Methodology for removing microplastics and other anthropogenic microparticles from sludge dewatering system

Anthropogenic microparticles (e.g., microplastics) are present in sewage plants, especially in sludge streams. However, the lack of standardized protocols to scrutinize the presence of anthropogenic microparticles in sludge makes the comparison between studies unfeasible. To tackle the knowledge gap regarding the efficiency of methodologies on the extraction of anthropogenic microparticles from the complex organic matrix, dewatered sludge, and digested sludge was treated with peroxidation and density separation, and the recovery of microparticles from these samples was investigated. The results showed that with the use of a higher density solution (NaI, 1.5 g/cm3) a much better recovery of anthropogenic microparticles from sludge samples (approximately 1000 microparticles/g-dw and 2000 microparticles/g-dw, from dewatered and digested sludge, respectively) was achieved in comparison with the use of a lower density solution (NaCl, 1.2 g/cm3) (200 microparticles/g-dw and 600 microparticles/g-dw from dewatered and digested sludge, respectively). Moreover, although the use of peroxidation is an essential step to break down the sludge structure and to release microparticles to the liquid phase, the use of peroxidation after or before density separation did not affect the overall recovery of microparticles. Polyethylene, polypropylene, and copolymer ethylene-ethyl-acrylate were the main microplastic fragments identified in digested sludge and dewatered sludge. However, no relation was observed between the method applied and the polymer recovered. Regarding the presence of anthropogenic microparticle in centrifuge effluent, 450 ± 212 microparticles/L were counted, and although little is known about this stream, in can be a relevant source of anthropogenic microparticles.

Calcium peroxide pre-treatment improved the anaerobic digestion of primary sludge and its co-digestion with waste activated sludge

Primary sludge (PS) and Waste activated sludge (WAS) as two main sludge streams in wastewater treatment plants are commonly anaerobically co-digested, which though may be differently affected by pretreatment. Previous work has found that calcium peroxide (CaO2) pretreatment effectively enhanced anaerobic digestion of WAS. However, the feasibilities of this strategy on PS anaerobic digestion and co-digestion of WAS and PS are still unclear. Herein, this work provided new insights into these systems. Biomethane potential test demonstrated that CaO2 pretreatment at 0.02–0.26 g/g-volatile suspended solids (VSS) promoted anaerobic digestion of PS. Then the feasibility of CaO2 pretreatment for improving anaerobic co-digestion of PS and WAS mixture was confirmed, with the highest improvement in methane production, VSS destruction and sludge reduction being approximately 37.4%, 38.9% and 19.9%, achieved at 0.14 g/g-VSS of CaO2. Process modelling analysis revealed that CaO2 pretreatment increased both degradable faction and actually degraded fraction in sludge mixture. The changes of sludge characteristics via pretreatment and key enzyme activity in sludge anaerobic co-digestion system demonstrated that increased CaO2 concentration resulted in increased soluble organics release from sludge mixture in the pretreatment stage and inhibited activity of coenzyme F420 responsible for methanogenesis. Further mechanism investigation disclosed that OH−, O2− and OH were main contribution factors, and the order of their contributions were OH− >O2− >OH. This work laid the theoretical foundation and provided guidance for the practical application of CaO2 pre-treatment technology.

Ionic strength of the liquid phase of different sludge streams in a wastewater treatment plant.

In a wastewater treatment plant (WWTP), several sludge streams exist and the composition of their liquid phase varies with time and place. For evaluating the potential for formation of precipitates and equilibria for weak acids/bases, the ionic strength and chemical composition need to be known. This information is often not available in literature, and even neglected in chemical model-based research. Based on a literature review, we proposed three ranges of concentration (low, typical and high) for the major constituents of the liquid phase of the different streams in a WWTP. The study also discusses the reasons for the concentration evolution, and the exceptional cases, to allow readers to consider the right range depending on their situation. The ionic strength of the different streams and the contribution of its constituents were calculated based on the ionic composition. The major contributors to the ionic strength for the wastewater-based streams (influent, effluent and mixed sludge) were Na+, Cl-, Mg2+ and Ca2+, representing 50-70% of the ionic strength. For digestate, NH4+ and HCO3- accounted for 65-75% of the ionic strength. Even though the ionic strength is recognized to impact several important wastewater treatment processes, its utilization in literature is not always adequate, which is discussed in this study.

A new utility-free circular integration approach for optimal multigeneration from biowaste streams

Traditional process integration approaches necessitate the allocation of external hot and cold utilities to avoid violating the Second Law of thermodynamics. Consequently, energy systems contribute significantly to anthropogenic climate change by emitting considerable greenhouse gases and losing substantial water for cooling in their hot and cold utilities, respectively. In this study, a new circular integration approach is proposed, which is used to model the first optimal multigeneration system independent of any external hot and cold utilities. The proposed approach is based on splitting a biowaste stream into two flows, one carbon rich and one water rich, and optimally recovering the feasible exergy according to the nexus between water, exergy, and carbon. To demonstrate this concept, municipal wastewater is split into carbon-rich sludge and water-rich effluent streams, and an efficient multigeneration system is modeled to optimally produce freshwater, power, cooling, heat, hydrogen, and oxygen with no external utilities. The system is optimally configured, sized, and operated in both hot and cold environments using the non-dominated sorting genetic algorithm III. The results show that the energy efficiency, exergy efficiency, and total annual costs of the optimal multigeneration system reached 79.4 % and 62.4 %, 49.98 % and 47.58 %, and US$158,000 and US$163,000 in cold and hot modes, respectively. According to an uncertainty analysis, the optimal system exhibited robust performance in both operating modes. It is anticipated that this breakthrough in sustainable engineering will mitigate anthropogenic climate change if applied extensively over the coming decades.

Novel semi-decentralised mobile system for the sanitization and dehydration of septic sludge: a pilot-scale evaluation in the Jordan Valley

The provision of effective sanitation strategies has a significant impact on public health. However, the treatment of septic sludge still presents some challenges worldwide. Consequently, innovative technologies capable of an effective and efficient sludge treatment, mostly at a decentralized level, are in high demand to improve sanitation provision. To address this problem, this study evaluates a novel semi-decentralised mobile faecal sludge treatment system, the pilot-system for which consists of a combination of several individual processes including mechanical dewatering (MD), microwave (MW) drying, and membrane filtration (ultrafiltration [UF] and reverse osmosis [RO]). The system evaluation was carried out by treating raw, partially digested faecal sludge (FS) from septic tanks—hence, septic sludge (SS)—in the Jordan Valley, Jordan. The pilot-scale system exhibited an effective and flexible treatment performance for (i) sanitizing faecal sludge and related liquid streams (MW and UF); (ii) reducing the treated sludge mass (and sludge volume) (MD and MW); and (iii) producing a high-quality treated liquid stream ideal for water reclamation applications (UF and RO). The MD process removed approximately 99% of the initial SS water content. The MW drying system completely removed E. coli and dehydrated the dewatered sludge at low energy expenditures of 0.75 MJ kg−1 and 5.5 MJ kg−1, respectively. Such energy expenditures can be further reduced by approximately 40% by recovering energy in the condensate and burning the dried sludge, which can then be reused inland applications. The membrane filtration system (UF and RO) was able to produce high-quality treated water that is ideal for the water reuse applications that irrigation requires, as well as meeting the Jordanian standard 893/2006. In addition, the system can also be powered by renewable energy sources, such as photovoltaic energy. Therefore, this research demonstrates that the evaluated semi-decentralised mobile system is technically feasible for the in situ treatment of SS (sanitization and dehydration), while also being effective for simultaneously recovering valuable resources, such as energy, water, and nutrients.

Organic matter parameters in WWTP - a critical review and recommendations for application in activated sludge modelling.

This paper includes a comprehensive literature review of sludge composition data from wastewater treatment plants. 722 data sets from 249 sources were used to establish typical ratios between COD and solids-based parameters and to verify rule-of-thumb values, respectively. Confirmation of these typical ratios can also be accomplished by using biochemical composition data. It is shown that a correlation between data from proteins, lipids and carbohydrates analysis can be related to COD/VSS ratios. Finally, using the findings from the literature review, the organic and inorganic conversion factors of COD fractions in activated sludge models are adjusted to solids-based parameters. It was shown that with the adjustments of the factors and a partition of the particulate inert fraction into a fraction assigned to the influent and a fraction assigned to the endogenous products, a better agreement with the ratios of COD/VSS in the individual sludge streams can be established.

Plant-wide investigation of sulfur flows in a water resource recovery facility (WRRF)

Even though sulfur compounds and their transformations may strongly affect wastewater treatment processes, their importance in water resource recovery facilities (WRRF) operation remains quite unexplored, notably when it comes to full-scale and plant-wide characterization. This contribution presents a first-of-a-kind, plant-wide quantification of total sulfur mass flows for all water and sludge streams in a full-scale WRRF. Because of its important impact on (post-treatment) process operation, the gaseous emission of sulfur as hydrogen sulfide (H2S) was also included, thus enabling a comprehensive evaluation of sulfur flows. Data availability and quality were optimized by experimental design and data reconciliation, which were applied for the first time to total sulfur flows. Total sulfur flows were successfully balanced over individual process treatment units as well as the plant-wide system with only minor variation to their original values, confirming that total sulfur is a conservative quantity. The two-stage anaerobic digestion with intermediate thermal hydrolysis led to a decreased sulfur content of dewatered sludge (by 36%). Higher (gaseous) H2S emissions were observed in the second-stage digester (42% of total emission) than in the first one, suggesting an impact of thermal treatment on the production of H2S. While the majority of sulfur mass flow from the influent left the plant through the treated effluent (> 95%), the sulfur discharge through dewatered sludge and gaseous emissions are critical. The latter are indeed responsible for odour nuisance, lower biogas quality, SO2 emissions upon sludge combustion and corrosion effects.

Performance of Anaerobic Membrane Bioreactors for the Co-digestion of Sewage Sludge and Food Waste

A laboratory-scale anaerobic membrane bioreactor (AnMBR) was used for the co-digestion of sewage sludge and food waste to investigate its organic matter removal characteristics, biogas production performance, and microbial community composition. The results showed that the degradation rate of volatile solids (VS) increased from 17.5% for a single digestion to 40% for the total digestion, and that the COD removal was 95.3% when the organic loading rate (OLR) was stabilized at 0.59-0.64 kg·(m3·d)-1. The solids content of the digested sludge increased by a factor of 3.9. The final CH4 content was 60% and the CH4 yield was 78.7 mL·g-1 of CODadded. The transmembrane pressure (TMP) and average flux were maintained at between -3.1 and -2.7 kPa and 0.106 L·(m2·h)-1, respectively, and membrane fouling was not serious. According to an analysis of the microbial diversity using 16S rRNA, the anaerobic bacterium in the AnMBR were mainly phylum Proteobacteria, Bacteroidetes, and Cloacimonetes, and the dominant methanogens included the Methanobacterium family, Methanosaeta genus, and Methanolinea genus. This study provides a strong theoretical basis for research into the stability and performance of AnMBRs for the co-treatment of sludge and other high-solid waste streams, and provided an effective solution for biomass resource utilization and the energy crisis.

Enhanced high-quality biomethane production from anaerobic digestion of primary sludge by corn stover biochar

This study conducted batch and continuous tests to reveal the feasibility of corn stover biochar on improving anaerobic digestion of primary sludge (PS). Dosing biochar (1.82, 2.55 and 3.06 g/g Total Solids (TS)) in digester improved methane content increasing from 67.5% to 81.3–87.3% and enhanced methane production by 8.6–17.8%. Model analysis indicated that biochar accelerated PS hydrolysis and enhanced methane potential of PS. The mechanistic studies showed that biochar enhanced process stability provided by strong buffering capacity and alleviated NH3 inhibition. In continuous test over 116 days, the volatile solids (VS) destruction in the biochar-dosed digester increased by 14.9%, resulting in a 14% reduction in the volume of digestate for disposal. Biochar changed microbial community in an expected direction for anaerobic digestion. This work suggests that biochar technology would apply to co-digestion of WAS and PS to maximize the energy recovery and sludge reduction from the two sludge streams.

Sludge Incineration Bottom Ash Enhances Anaerobic Digestion of Primary Sludge toward Highly Efficient Sludge Anaerobic Codigestion

In wastewater treatment plants (WWTPs), two main sludge streams, i.e., primary sludge (PS) and waste activated sludge (WAS), are generally mixed for anaerobic codigestion. However, the methane prod...

Effects of dosing iron- and alum-containing waterworks sludge on sulfide and phosphate removal in a pilot sewer

Reusing waterworks aluminium (Al)- or iron (Fe)-sludge instead of chemical coagulants such as Al- or Fe-salts, is a credible solution for sulfide and phosphate control in sewer bulk phase for environmental and economic reasons. We comprehensively evaluated and compared the effects of direct dosing of waterworks Fe-/Al-sludge in pilot-scale sewer rising mains, particularly focusing on removal of sulfides and phosphate and underlying possible mechanisms. Changes in other sewage characteristics were also examined. Waterworks Fe-sludge dosing was effective for sulfide removal at a ratio of 0.29 ± 0.06 mg S/mg Fe, but exhibited limited effect on phosphate removal. Likewise, Al-sludge was effective for phosphate removal at ratio of 0.29 ± 0.01 mg P/mg Al, but with limited effect on sulfide removal. The mixing of the sludge stream with raw wastewater, i.e. dilution effect, was primarily responsible for observed reduction in soluble chemical oxygen demand (sCOD) concentrations, under both Fe-/Al-sludge dosing. The Fe-/Al-sludge dosing did not cause any increment in dissolved methane (CH4) and nitrous oxide (N2O) formation, nor release of other metals. Combined spectroscopic, spectrometric, and microscopic analyses suggest a precipitation reaction between sulfide and ferric ions in Fe-sludge, is likely to be the dominant mechanism for sulfide removal when dosing Fe-sludge. In terms of phosphate removal with Al-sludge dosing, ligand-exchange processes between surface hydroxyl (–OH) groups and PO43− ions, favouring the formation of both inner- and outer-sphere surface Al-phosphate complexes, appears to be the dominant mechanism. These findings showed the potential multiple benefits of dosing waterworks Fe-/Al-sludge in sewers. Further system-wide, long-term studies including a comprehensive cost-benefit analysis are warranted for optimisation.

Novel clinically relevant antibiotic resistance genes associated with sewage sludge and industrial waste streams revealed by functional metagenomic screening

A growing body of evidence indicates that anthropogenic activities can result in increased prevalence of antimicrobial resistance genes (ARGs) in bacteria in natural environments. Many environmental studies have used next-generation sequencing methods to sequence the metagenome. However, this approach is limited as it does not identify divergent uncharacterized genes or demonstrate activity. Characterization of ARGs in environmental metagenomes is important for understanding the evolution and dissemination of resistance, as there are several examples of clinically important resistance genes originating in environmental species. The current study employed a functional metagenomic approach to detect genes encoding resistance to extended spectrum β-lactams (ESBLs) and carbapenems in sewage sludge, sludge amended soil, quaternary ammonium compound (QAC) impacted reed bed sediment and less impacted long term curated grassland soil. ESBL and carbapenemase genes were detected in sewage sludge, sludge amended soils and QAC impacted soil with varying degrees of homology to clinically important β-lactamase genes. The flanking regions were sequenced to identify potential host background and genetic context. Novel β-lactamase genes were found in Gram negative bacteria, with one gene adjacent to an insertion sequence ISPme1, suggesting a recent mobilization event and/ the potential for future transfer. Sewage sludge and quaternary ammonium compound (QAC) rich industrial effluent appear to disseminate and/or select for ESBL genes which were not detected in long term curated grassland soils. This work confirms the natural environment as a reservoir of novel and mobilizable resistance genes, which may pose a threat to human and animal health.

Novel Use of Dairy Processing Sludge Derived Pyrogenic Char (DPS-PC) to Remove Phosphorus in Discharge Effluents

Pyrogenic char (PC) materials derived from the pyrolysis of dairy processing sludge (DPS) could be a cost effective option to develop carbonaceous adsorbent for phosphorus (P) removal from wastewater. The main objectives of the present work were to: (1) determine the efficacy of DPS derived PC (DPS-PC) to remove P from synthetic and dairy wastewater samples, (2) identify possible P removal mechanisms, and identify parameters that could be used to quickly identify the P removal capacity of a char and (3) propose a ranking system for the selection of DPS-PC which includes energy, char yield and P removal criterion. DPS-PC samples were obtained from the pyrolysis process (700 °C) of two sludge streams: (1) bio-chemically treated mixed sludge and (2) lime treated dissolved air floatation (DAF) sludge. Herein, 12 DPS-PC samples were assessed and pre-screened in batch experiments to determine the P removal efficacy from both synthetic and dairy wastewater solutions. The effect of solid to liquid dosage, contact time, pH and P concentration was investigated. Statistical regression and correlation analyses were performed to understand P removal mechanism. The quantitative assessment of char yield, energy balance and P removal performance were combined to propose a ranking system for DPS feedstock selection. P removal varied across DPS-PC type and composition, with mixed sludge derived char exhibiting 85–98% P removal at a dose of between 10 and 50 g/L, whereas, those from DAF sludge removed > 99% at 3 g/L. The P removal process was associated with a number of strongly significant mineral phase correlations pertaining to mineral composition (i.e. availability of Ca, Mg and Si) of the DPS-PC samples. A quick water extractible P test together with knowledge of the major P locking minerals can be used to pre-screen the potential of PC for P removal application. This study also provides a physicochemical reference and ranking of DPS feedstock selection, which will be useful for future investigation on the pyrolysis of DPS at pilot-scale and subsequently, to develop PC based efficient adsorbent for application in wastewater treatment.