Economical and ecological comparison of granular activated carbon (GAC) adsorber refill strategies

Biochar from recovered cellulose as new admixture in constructed wetlands for micropollutant removal: A circular approach

This study aimed to evaluate the suitability of biochar produced by pyrolysis from recovered wastewater cellulose and activated biologically as an admixture in Constructed Wetlands (CWs) when applied as a post-treatment step to remove micropollutants (MPs) from municipal wastewater effluent. Two planted vertical flow mesocosm CWs with cellulose-based admixtures of different origins (plant residue and recovered toilet paper) were fed with a municipal wastewater effluent representative for rural catchments. The results showed an average MPs elimination of 89.1 % for the activated biochar produced from recovered cellulose when 15 relevant compounds are considered and a reduction of the risk from compounds cocktail below the maximum acceptable level having diclofenac, carbamazepine, PFOS, ciprofloxacin and clarithromycin as main risk drivers (Risk Quotient > 1). The implementation of a circular approach to reduce MPs was finally conducted for the Blies catchment (Saarland region in Germany) characterized by low population density and small, sensitive water bodies. This approach demonstrates the feasibility of combining cellulose recovery with a fine sieve in large wastewater treatment plants (WWTPs) and providing biochar produced from recovered cellulose as an admixture to small WWTP where CW is an affordable solution for MP mitigation.

Overview of environmental and economic viability of activated carbons derived from waste biomass for adsorptive water treatment applications

In adsorptive water treatment applications, the exploration of waste-derived activated carbon (AC) has gained substantial attention in scientific research. The use of waste materials as precursors for AC has gained attention due to its economic viability and potential to reduce the consumption of non-renewable resources. However, there is a lack of comprehensive literature regarding the costs and environmental impacts associated with the waste-based AC production and application. As sustainability practices gain importance, there has been an increase in research dedicated to estimating costs and conducting life cycle assessment (LCA) of AC production from waste sources. However, there is a need for thorough literature reviews that cover various methodologies and conclusions. The primary objective of this study is to provide a comprehensive overview and analysis of the economic and environmental factors related to the use of waste-derived AC in water treatment. LCA studies indicate that utilizing waste materials for AC production can lead to significant resource and energy savings compared to conventional methods relying on fossil resources. The cost of AC is influenced by factors such as precursor material cost, energy requirements during production (optimizable on an industrial scale), and properties of the resulting material. Additionally, the review emphasizes the significance of waste-based AC regeneration for sustainable viability. Evaluating the environmental and economic costs is crucial to support sustainability claims and avoid unsupported assertions. Overall, this study contributes to understanding the potential of waste-derived AC in water treatment and highlights the need for further research in this area.

Comparative life cycle assessment of activated carbon production from various raw materials

Activated carbon (AC) is an effective adsorbent in water treatment but its production method has significant emissions to the environment. This study aims to quantify the environmental impacts of various AC types and determine whether raw material selection could reduce the footprint of AC. A cradle-to-gate life cycle assessment (LCA) was conducted on coal, coconut shell, wood, peat, and reactivated coal ACs. The different types of raw materials were selected to reflect typical global and local availability in the selected location. Life cycle data was collected from the Ecoinvent database, scientific literature, and an industrial producer. Using CML 2001 as a characterization method, potential environmental impacts were calculated for 12 categories. The direct emissions of AC production and electricity production were the largest contributors to environmental impacts. Coal AC had the highest impact in ten out of the twelve categories. On the other hand, reactivated coal and coconut AC had the lowest impacts in three and five categories, respectively. The comparison in carbon footprints between the AC types were found to be dependent on inclusion or exclusion of biogenic emissions: When including biogenic carbon emissions, the Global Warming Potential (GWP) of reactivated coal AC was 72-80% lower than for the virgin ACs. When biogenic carbon emissions were excluded, the GWPs of the residual biomass ACs (coconut shell and wood) were found to be about 50% lower than that of reactivated coal AC. The results demonstrate that raw material choice and production method significantly affect the environmental impact of AC. To minimize site-specific impacts of AC application, technical feasibility of AC and use phase emissions need to be assessed.

Sand and sand-GAC filtration technologies in removing PPCPs: A review

Concerns have been raised about the risks that pharmaceuticals and personal care products (PPCPs) in aquatic environments posed to humans and the environment. In recent years, sand filtration has been used to potentially remove these emerging contaminants from water. However, there has been no review of the effectiveness of this technology to date. This paper presents a brief introduction of sand filtration types, reviews the current progress in PPCPs removal through sand filtration, and discusses the mechanisms behind this process and the combination of granular activated carbon (GAC) and sand as an enhanced sand-GAC filtration technology. Sand filtration achieves a reasonable but highly variable degree of PPCPs removal. Biodegradation and adsorption are the two main mechanisms of PPCPs removal, in particular the biodegradation since adsorption capacity of sand is relatively low. Other processes, such as bio-sorption and indirect adsorption, may also contribute to PPCPs removal. To compensate for the inadequate PPCPs removal through sand filtration, porous GAC has been combined with sand to develop sand-GAC filtration technologies. Serial, dual, and sandwich filters have been investigated, and significant removal enhancement has been observed, due to the strengthened adsorption capacity, suggesting the applicability of these variants. Future research focus, such as investigating the influence of different operational conditions on sand filter performance, obtaining a deeper understanding of the various removal mechanisms, and investigating of long-term performance of the filter used for PPCPs removal, are suggested.

Conversion of Waste Biomass into Activated Carbon and Evaluation of Environmental Consequences Using Life Cycle Assessment

In this article, activated carbon was produced from Lantana camara and olive trees by H3PO4 chemical activation. The prepared activated carbons were analyzed by characterizations such as scanning electron microscopy, energy-dispersive X-ray spectroscopy, Brunauer–Emmett–Teller, X-ray diffraction, thermogravimetric analysis, and Fourier transform infrared spectroscopy. H3PO4 is used as an activator agent to create an abundant pore structure. According to EDX analysis, the crystalline structure destroys and increases the carbon content of the olive tree and Lantana camara by 77.51 and 76.16%, respectively. SEM images reveal a porous structure formed as a result of H3PO4 activation. The Brunauer–Emmett–Teller (BET) surface area of the olive tree and Lantana camara activated carbon was 611.21 m2/g and 167.47 m2/g, respectively. The TGA analysis of both activated carbons shows their thermal degradation starts at 230 °C but fully degrades at temperatures above 450 °C. To quantify the potential environmental implications related to the production process of the activated carbon (AC) from olive trees, the life cycle assessment (LCA) environmental methodology was employed. For most of the tested indicators, chemical activation using H3PO4 showed the greatest ecological impacts: the ozone layer depletion potential (42.27%), the acidification potential (55.31%), human toxicity (57.00%), freshwater aquatic ecotoxicity (85.01%), terrestrial ecotoxicity (86.17%), and eutrophication (92.20%). The global warming potential (5.210 kg CO2 eq), which was evenly weighted between the phases, was shown to be one of the most significant impacts. The total energy demand of the olive tree’s AC producing process was 70.521 MJ per Kg.

New directions and challenges in engineering biologically-enhanced biochar for biological water treatment

Cost-effective, efficient, and sustainable water treatment solutions utilising existing materials and technology will make it easier for low and middle-income countries to adopt them, improving public health. The ability of biochar to mediate and support microbial degradation of contaminants, combined with its carbon-sequestration potential, has attracted attention in recent years. Biochar is a possible candidate for use in cost-effective and sustainable biological water treatment, especially in agrarian economies with easy access to abundant biomass in the form of crop residues and organic wastes. This review evaluates the scope, potential benefits (economic and environmental) and challenges of sustainable biological water treatment using 'Biologically-Enhanced Biochar' or BEB. We discuss the various processes occurring in BEB systems and demonstrate the urgent need to investigate microbial degradation mechanisms. We highlight the need to correlate biochar properties to biofilm development, which can eventually determine process efficiency. We also demonstrate the various opportunities in adopting BEB as a cheaper and more viable alternative in Low and Middle Income Countries and compare it to the current benchmark, 'Biological Activated Carbon'. We focus on the recent advances in the areas of data science, mathematical modelling and molecular biology to systematically and sustainably design BEB filters, unlike the largely empirical design approaches seen in water treatment. 'Sequential biochar systems' are introduced as specially designed end-of-life techniques to lower the environmental impact of BEB filters and examples of their integration into biological water treatment that can fulfil zero waste criteria for BEBs are given.

Removal of contaminants of emerging concern from multicomponent systems using carbon dioxide activated biochar from lignocellulosic feedstocks

Adsorption of six contaminants of emerging concern (CECs) - caffeine, chloramphenicol, carbamazepine, bisphenol A, diclofenac, and triclosan - from a multicomponent solution was studied using activated biochars obtained from three lignocellulosic feedstocks: wheat straw, softwood, and peach stones. Structural parameters related to the porosity and ash content of activated biochar and the hydrophobic properties of the CECs were found to influence the adsorption efficiency. For straw and softwood biochar, activation resulted in a more developed mesoporosity, whereas activation of peach stone biochar increased only the microporosity. The most hydrophilic CECs studied, caffeine and chloramphenicol, displayed the highest adsorption (22.8 and 11.3 mg g^-1) onto activated wheat straw biochar which had the highest ash content of the studied adsorbents (20 wt%). Adsorption of bisphenol A and triclosan, both relatively hydrophobic substances, was highest (31.6 and 30.2 mg g^-1) onto activated biochar from softwood, which displayed a well-developed mesoporosity and low ash content.

Protein nanofibrils for next generation sustainable water purification

Water scarcity is rapidly spreading across the planet, threatening the population across the five continents and calling for global sustainable solutions. Water reclamation is the most ecological approach for supplying clean drinking water. However, current water purification technologies are seldom sustainable, due to high-energy consumption and negative environmental footprint. Here, we review the cutting-edge technologies based on protein nanofibrils as water purification agents and we highlight the benefits of this green, efficient and affordable solution to alleviate the global water crisis. We discuss the different protein nanofibrils agents available and analyze them in terms of performance, range of applicability and sustainability. We underline the unique opportunity of designing protein nanofibrils for efficient water purification starting from food waste, as well as cattle, agricultural or dairy industry byproducts, allowing simultaneous environmental, economic and social benefits and we present a case analysis, including a detailed life cycle assessment, to establish their sustainable footprint against other common natural-based adsorbents, anticipating a bright future for this water purification approach.

Electrochemical regeneration of spent activated carbon from drinking water treatment plant at different scale reactors

The electrochemical regeneration of real spent activated carbons (AC) used in drinking water treatment plants was studied at different reactor scales. The electrochemical regeneration was carried out in a 6 g filter-press cell and a 3.5 kg batch reactor, allowing the scaling-up of the process between the two electrolytic reactors. The effect of the electrolyte, the divided/undivided compartment configuration and the current density were studied in the filter-press cell. The effect of compartment configuration and the influence of the regeneration time were studied in the scaled-up reactor. A current density of 0.025 A cm^-2 was used and the electrodes were Pt/Ti as anode and Pt/Ti and stainless-steel as cathode. The ACs were characterized by N₂ adsorption isotherms to analyse the recovery of porosity and TPD-MS to analyse the AC surface after the electrochemical treatment. In filter-press cell, a recovery of the surface area of 96% was achieved after 8 h of treatment, by introducing the AC in the cathodic compartment using 0.05 M H₂SO₄ solution as electrolyte. In the 3.5 kg electrochemical reactor, 95% of the pristine AC surface area was recovered. Thus, electrochemical methods can provide a green alternative to the regeneration of spent AC.

Chemical enhanced oil recovery and the dilemma of more and cleaner energy

A method based on the concept of exergy-return on exergy-investment is developed to determine the energy efficiency and CO₂ intensity of polymer and surfactant enhanced oil recovery techniques. Exergy is the useful work obtained from a system at a given thermodynamics state. The main exergy investment in oil recovery by water injection is related to the circulation of water required to produce oil. At water cuts (water fraction in the total liquid produced) greater than 90%, more than 70% of the total invested energy is spent on injection and lift pumps, resulting in large CO₂ intensity for the produced oil. It is shown that injection of polymer with or without surfactant can considerably reduce CO₂ intensity of the mature waterflood projects by decreasing the volume of produced water and the exergy investment associated with its circulation. In the field examples considered in this paper, a barrel of oil produced by injection of polymer has 2–5 times less CO₂ intensity compared to the baseline waterflood oil. Due to large manufacturing exergy of the synthetic polymers and surfactants, in some cases, the unit exergy investment for production of oil could be larger than that of the waterflooding. It is asserted that polymer injection into reservoirs with large water cut can be a solution for two major challenges of the energy transition period: (1) meet the global energy demand via an increase in oil recovery and (2) reduce the CO₂ intensity of oil production (more and cleaner energy).

Life Cycle Assessment of Urine Diversion and Conversion to Fertilizer Products at the City Scale

Urine diversion has been proposed as an approach for producing renewable fertilizers and reducing nutrient loads to wastewater treatment plants. Life cycle assessment was used to compare environmental impacts of the operations phase of urine diversion and fertilizer processing systems [via (1) a urine concentration alternative and (2) a struvite precipitation and ion exchange alternative] at a city scale to conventional systems. Scenarios in Vermont, Michigan, and Virginia were modeled, along with additional sensitivity analyses to understand the importance of key parameters, such as the electricity grid and wastewater treatment method. Both urine diversion technologies had better environmental performance than the conventional system and led to reductions of 29-47% in greenhouse gas emissions, 26-41% in energy consumption, approximately half the freshwater use, and 25-64% in eutrophication potential, while acidification potential ranged between a 24% decrease to a 90% increase. In some situations, wastewater treatment chemical requirements were eliminated. The environmental performance improvement was usually dependent on offsetting the production of synthetic fertilizers. This study suggests that urine diversion could be applied broadly as a strategy for both improving wastewater management and decarbonization.

Natural clay as a sorbent to remove pharmaceutical micropollutants from wastewater

Worldwide, the aquatic environment is contaminated by micro-pollutants, such as ingredients of personal care products, pesticides and pharmaceuticals. This contamination is one of the major environmental issues of global concern. Adsorption is one of approach, which has been most extensively discussed within recent years for the reduction of the input of micro-pollutants into the environment. In the present study, the natural clay classified as Na-montmorillonite, was characterized and tested for its potential to remove four model compounds representing different polarity and ionizability: i) diatrizoic acid (DAT), ii) iopamidol (IOP), iii) metformin (MTF), and iv) carbamazepine (CBZ). The adsorption efficiency of clay was evaluated by initial compound concentration, effect of pH, contact time and temperature. The results indicated that clay was able to remove the pharmaceuticals from aqueous medium with an efficiency of 70% for CBZ and MTF. In contrast, clay showed a lower removal of 30% for DAT and no removal for IOP. The results indicate that clay could rapidly and efficiently reduce the concentration of CBZ and MTF, which could provide a solution to remove some substances, without undesirable by-product generation. However, this study clearly demonstrated that removal rates strongly depend on the compound. Albeit chemical structure may play a role for the different degree of removal, this study could not completely explain the sorption mechanism between sorbent-sorbate interactions.

The synthesis strategy to enhance the performance and cyclic utilization of granulated activated carbon-based sorbent for bisphenol A and triclosan removal

For a potential and efficient solution in the mitigation of aquatic pollution, this study reported a well-designed and developed protected granulated activated carbon (GAC) material which ensures high strength property and adsorption performance to meet the industrial application. The prepared GAC material was shaped into a spherical core using natural binders basically assumed to constitute waste solids materials. Then after, the granulated carbon core (GAC core) was protected by a porous ceramic shell which confined the material with strong protection and high mechanical strength to resist against degeneration and pressure drop as a limiting factor for most sorbents employed in solution. The CSGAC characterization results proved that the ceramic shell has a smaller thickness (0.1 cm), good mechanical strength (2.0 MPa), and additionally, it presents larger porous channels which promote the fast and higher adsorption performance making it the desired material for the application in the real liquid environment. The test results showed that the prepared material had higher removal of triclosan (TCS) (30-40 mg/L) than BPA counterpart from the aqueous solutions. Moreover, it showed higher adsorption performance compared to the unprotected carbon materials. Furthermore, the mechanisms of BPA and TCS adsorption by core-shell granulated activated carbon (CSGAC) were discussed.

Chemical or Natural? Including LCA in Social CBA to Compare Remediation Alternatives for a Dry-Cleaning Facility

The choice between remediation alternatives for contaminated sites is complicated by different elements, e.g., the occurrence of multiple contaminants, the extent of the contamination, or the urban location, complicate the choice between remediation alternatives. This paper addresses this challenging choice by analyzing a case study of an extensive soil and groundwater contamination by a dry-cleaning company. For remediating this site, two alternatives were proposed. The first remediation alternative combines several techniques with in-situ chemical oxidization being the most important one. Due to the potential negative impact of this alternative on local residents a second remediation alternative was drawn up, in which the focus lies on the use of stimulated biological degradation. A Life Cycle Assessment (LCA) was performed on both alternatives and showed that the second alternative had a lower environmental impact. The inclusion of monetized LCA results in the calculation of a social Cost-Benefit Analysis (CBA) provided a more extensive view of the secondary environmental costs and benefits of the remediation alternatives. The results of the social CBA allow to conclude that both alternatives are not socially desirable, the chemical alternative however is socially less disadvantageous than the more natural remediation alternative.

Life cycle environmental and economic implications of small drinking water system upgrades to reduce disinfection byproducts

Many of the small drinking water systems in the US that utilize simple filtration and chlorine disinfection or chlorine disinfection alone are facing disinfection byproduct (DBP) noncompliance issues, which need immediate upgrades. In this study, four potential upgrade scenarios, namely the GAC, ozone, UV30, and UV186 scenarios, were designed for a typical small drinking water systems and compared in terms of embodied energy, carbon footprint, and life cycle cost. These scenarios are designed to either reduce the amount of DBP precursors using granular activated carbon filtration (the GAC scenario) or ozonation (the ozone scenario), or replace the chlorine disinfection with the UV disinfection at different intensities followed by chloramination (the UV30 and UV186 scenarios). The UV30 scenario was found to have the lowest embodied energy (417 GJ/year) and life cycle cost ($0.25 million US dollars), while the GAC scenario has the lowest carbon footprint (21 Mg CO₂e/year). The UV186 scenario consistently presents the highest environmental and economic impacts. The major contributors of the economic and environmental impacts of individual scenarios also differ. Energy and/or material consumptions during the operation phase dominate the environmental impacts of the four scenarios, while the infrastructure investments have a noticeable contribution to the economic costs. The results are sensitive to changes in water quality. An increase of raw water quality, i.e., an increase in organic precursor content, could potentially result in the ozone scenario being the least energy intensive scenario, while a decrease of water quality could greatly reduce the overall competitiveness of the GAC scenario.

Life cycle environmental impacts of advanced wastewater treatment techniques for removal of pharmaceuticals and personal care products (PPCPs)

Pharmaceutical and personal care products (PPCPs) are of increasing interest because of their ecotoxicological properties and environmental impacts. Wastewater treatment plants (WWTPs) are the main pathway for their release into freshwaters due to the inefficiency of conventional WWTPs in removing many of these contaminants from effluents. Therefore, different advanced effluent treatment techniques have been proposed for their treatment. However, it is not known at present how effective these treatment methods are and whether on a life cycle basis they cause other environmental impacts which may outweigh the benefits of the treatment. In an effort to provide an insight into this question, this paper considers life cycle environmental impacts of the following advanced treatment techniques aimed at reducing freshwater ecotoxicity potential of PPCPs: granular activated carbon (GAC), nanofiltration (NF), solar photo-Fenton (SPF) and ozonation. The results suggest that on average NF has the lowest impacts for 13 out of 18 categories considered. GAC is the best alternative for five impacts, including metals and water depletion, but it has the highest marine eutrophication. SPF and ozonation are the least sustainable for eight impacts, including ecotoxicity and climate change. GAC and NF are also more efficient in treating heavy metals while avoiding generation of harmful by-products during the treatment, thus being more suitable for potable reuse of wastewater. However, releasing the effluent without advanced treatment to agricultural land achieves a much higher reduction of freshwater ecotoxicity than treating it by any of the advanced treatments and releasing to the environment. Therefore, the use of advanced effluent treatment for agricultural purposes is not recommended.

Friends or foes? Monetized Life Cycle Assessment and Cost-Benefit Analysis of the site remediation of a former gas plant

Site contamination is a global concern because of the potential risks for human health and ecosystem quality. Every contaminated site has its own specific characteristics and the increased availability and efficiency of remediation techniques makes the choice of remediation alternative increasingly complicated. In this paper an attributional Life Cycle Assessment (LCA) of the secondary environmental impacts of a site remediation is performed and its results are monetized using two different monetization techniques, namely Stepwise 2006 and Ecovalue 08. Secondly, we perform a social Cost-Benefit Analysis (CBA) on the same case study using the same data sources. The case study used in this paper entails the soil and groundwater remediation of a tar, poly-aromatic hydrocarbons (PAH) and cyanide contamination of a school ground by a former gas plant. The remediation alternative chosen in this case study is excavation with off-site thermal treatment of the contaminated soil. The outcome of the social CBA, stating that the remediation project is socially beneficial in the long term, is critically compared to the outcome of the different LCA monetization methods. This comparison indicates that monetized LCA is a good complement to social CBA when it comes to the assessment of secondary environmental impacts. Combining the two methods provides decision makers with a more extensive and detailed assessment of the soil remediation project.

Technical-environmental optimisation of the activated carbon production of an agroindustrial waste by means response surface and life cycle assessment

In this study, a simultaneous optimisation of technical and environmental parameters for activated carbon production from soybean shells is presented. A 2³ factorial design was developed to explore the performance of the technical responses yield and iodine number, and the single score of ReCiPe endpoint method, which was evaluated by means the life cycle assessment. The independent factors included in the design of experiments were the impregnation ratio, temperature, and time activation. Three quadratic equations were obtained and simultaneously optimised by maximisation of the overall desirability function. The principal results of the individual responses indicate that the iodine number is practically independent of the activation temperature in a range of 450 ºC-650 ºC; the yield is inversely proportional to activation time and exhibits minimum values between 500 ºC-600 ºC; and the environmental response single score presents the lowest value at a temperature and time activation of 450 ºC and 30 min, respectively. The most polluting stage of activated carbon production from soybean shells production is the impregnation stage, mainly for the use of ZnCl₂ as activating agent and the energy consumption. The simultaneous optimisation of the three responses indicates that the optimal activated carbon should be produced at 180 min, 650 ºC, and an impregnation ratio of 1 g soybean shell g ZnCl₂^-1.

Energy demand for elimination of organic micropollutants in municipal wastewater treatment plants

Organic micropollutants (OMP), e.g. pharmaceuticals and household/industrial chemicals, are not fully eliminated in state-of-the-art municipal wastewater treatment plants and can potentially harm the aquatic environment. Therefore, several pilot and large-scale investigations on the elimination of organic micropollutants have taken place in recent years. Based on the present findings, the most efficient treatment steps to eliminate organic micropollutants have proven to be ozonation, adsorption on powdered activated carbon (PAC), or filtration through granular activated carbon (GAC). Yet a further treatment step implies an increase in energy demand of the wastewater treatment plant, which has to be considered along with OMP elimination. To this aim, data on energy demand of ten large-scale municipal wastewater treatment plants (WWTP) with processes for OMP elimination was collected and analyzed. Moreover, calculations on energy demand beyond the WWTP for production and transport of ancillary materials were performed to assess the cumulative energy demand of the processes. An assessment of the greenhouse gas emissions of the processes was achieved, which shall facilitate future life cycle analyses. The results show that energy demand of ozonation at the wastewater treatment plant is dependent upon the ozone dosage and is significantly higher than energy demand of PAC addition or GAC filtration (2 to 4 times higher without consideration of delivery heads). Despite uncertainties regarding the energy demand for production of activated carbon, it could be shown that the cumulative energy demand of adsorption steps is significantly higher than the energy demand at the WWTP. Using reactivated GAC can lead to energy and greenhouse gas emissions savings compared to using fresh GAC/PAC. Moreover, energy demand is always plant-specific and depends on different factors (delivery heads, existing filtration or post-treatment etc.). Since processes for elimination of organic micropollutants are still in a developing phase, future optimization steps shall minimize their energy demand.

Environmental Comparison of Biochar and Activated Carbon for Tertiary Wastewater Treatment

Micropollutants in wastewater present environmental and human health challenges. Powdered activated carbon (PAC) can effectively remove organic micropollutants, but PAC production is energy intensive and expensive. Biochar adsorbents can cost less and sequester carbon; however, net benefits depend on biochar production conditions and treatment capabilities. Here, life cycle assessment was used to compare 10 environmental impacts from the production and use of wood biochar, biosolids biochar, and coal-derived PAC to remove sulfamethoxazole from wastewater. Moderate capacity wood biochar had environmental benefits in four categories (smog, global warming, respiratory effects, noncarcinogenics) linked to energy recovery and carbon sequestration, and environmental impacts worse than PAC in two categories (eutrophication, carcinogenics). Low capacity wood biochar had even larger benefits for global warming, respiratory effects, and noncarcinogenics, but exhibited worse impacts than PAC in five categories due to larger biochar dose requirements to reach the treatment objective. Biosolids biochar had the worst relative environmental performance due to energy use for biosolids drying and the need for supplemental adsorbent. Overall, moderate capacity wood biochar is an environmentally superior alternative to coal-based PAC for micropollutant removal from wastewater, and its use can offset a wastewater facility's carbon footprint.

4-MCHM sorption to and desorption from granular activated carbon and raw coal

4-Methylcyclohexanemethanol (4-MCHM) is a saturated higher alicyclic primary alcohol that is used in the froth flotation process for cleaning coal. In early 2014, a large spill of crude chemical (containing primarily 4-MCHM) to the Elk River near Charleston, WV contaminated the local water supply. Carbon filters at the affected water treatment facility quickly became saturated, and the contaminated water was distributed to nearby homes and businesses. Sorption of 4-MCHM to granular activated carbon (GAC) was studied in the laboratory using head space (HS) analysis via gas chromatography with a flame ionization detector (GC-FID). Sorption to raw coal was also investigated, since this material may be of interest as a sorbent in the case of an on-site spill. As expected, sorption to both materials increased with decreased particle size and with increased exposure time; although exposure time proved to be much more important in the case of GAC than for coal. Under similar conditions, GAC sorbed more 4-MCHM than raw coal (e.g., 84.9 vs. 63.1 mg/g, respectively, for 20 × 30 mesh particles exposed to 860 mg/L 4-MCHM solution for 24 h). Desorption from both materials was additionally evaluated. Interestingly, desorption of 4-MCHM on a mass per mass basis was also higher for GAC than for raw coal. Overall, results indicated that GAC readily sorbs 4-MCHM but can also readily release a portion of the chemical, whereas coal sorbs somewhat less 4-MCHM but holds it tightly.

Secondary environmental impacts of remedial alternatives for sediment contaminated with hydrophobic organic contaminants

This study evaluates secondary environmental impacts of various remedial alternatives for sediment contaminated with hydrophobic organic contaminants using life cycle assessment (LCA). Three alternatives including two conventional methods, dredge-and-fill and capping, and an innovative sediment treatment technique, in-situ activated carbon (AC) amendment, are compared for secondary environmental impacts by a case study for a site at Hunters Point Shipyard, San Francisco, CA. The LCA results show that capping generates substantially smaller impacts than dredge-and-fill and in-situ amendment using coal-based virgin AC. The secondary impacts from in-situ AC amendment can be reduced effectively by using recycled or wood-based virgin AC as production of these materials causes much smaller impacts than coal-based virgin AC. The secondary environmental impacts are highly sensitive to the dredged amount and the distance to a disposal site for dredging, the capping thickness and the distance to the cap materials for capping, and the AC dose for in-situ AC amendment. Based on the analysis, this study identifies strategies to minimize secondary impacts caused by different remediation activities: optimize the dredged amount, the capping thickness, or the AC dose by extensive site assessments, obtain source materials from local sites, and use recycled or bio-based AC.

Anaerobic digestion of post-hydrothermal liquefaction wastewater for improved energy efficiency of hydrothermal bioenergy processes

Hydrothermal liquefaction (HTL) is a promising process for converting wet biomass and organic wastes into bio-crude oil. It also produces an aqueous product referred to as post-hydrothermal liquefaction wastewater (PHWW) containing up to 40% of the original feedstock carbon, which reduces the overall energy efficiency of the HTL process. This study investigated the feasibility of using anaerobic digestion (AD) to treat PHWW, with the aid of activated carbon. Results showed that successful AD occurred at relatively low concentrations of PHWW (≤ 6.7%), producing a biogas yield of 0.5 ml/mg CODremoved, and ∼53% energy recovery efficiency. Higher concentrations of PHWW (≥13.3%) had an inhibitory effect on the AD process, as indicated by delayed, slower, or no biogas production. Activated carbon was shown to effectively mitigate this inhibitory effect by enhancing biogas production and allowing digestion to proceed at higher PHWW concentrations (up to 33.3%), likely due to sequestering toxic organic compounds. The addition of activated carbon also increased the net energy recovery efficiency of AD with a relatively high concentration of PHWW (33.3%), taking into account the energy for producing activated carbon. These results suggest that AD is a feasible approach to treat PHWW, and to improve the energy efficiency of the HTL processes.

Analysis of good practices, barriers and drivers for ELTs pyrolysis industrial application

Boosting of eco-innovative solutions for End of Life Tyres (ELTs) management, under the principles of the EU Resource Efficiency Roadmap and the Waste Framework Directive, can not only diminish the environmental hazards and the consequent societal cost, but also result to the establishment of a novel perception regarding ELTs; thus, a valuable stock of resources that can be exploited. Despite the extensive scientific research of the previous years on ELTs depolymerisation via pyrolysis highlighting its eco-innovative characteristics, the use of pyrolysis to process scrap tyres has not yet achieved a broad commercial success, with economic viability and product standardization to constitute the primary impediments. More specifically, pyrolysis was not applied to an extensive industrial scale so far, due to deficient market analysis, legislative barriers, economic instability and sometimes public acceptance. All the above issues are addressed by the present study. Modifications on current EU legislation can prevent or reduce delays or derailment of efforts on pyrolysis, through its differentiation from incineration. The attainment of economic viability could be realized through the valorization of the pyrolytic char towards activated carbon production for environmental depollution applications; needless to say, the penetration on niche and well-organised markets is more than essential.

Environmental impact associated with activated carbon preparation from olive-waste cake via life cycle assessment

The life cycle assessment (LCA) environmental tool was implemented to quantify the potential environmental impacts associated with the activated carbon (AC) production process from olive-waste cakes in Tunisia. On the basis of laboratory investigations for AC preparation, a flowchart was developed and the environmental impacts were determined. The LCA functional unit chosen was the production of 1 kg of AC from by-product olive-waste cakes. The results showed that impregnation using H3PO4 presented the highest environmental impacts for the majority of the indicators tested: acidification potential (62%), eutrophication (96%), ozone depletion potential (44%), human toxicity (64%), fresh water aquatic ecotoxicity (90%) and terrestrial ecotoxicity (92%). One of the highest impacts was found to be the global warming potential (11.096 kg CO2 eq/kg AC), which was equally weighted between the steps involving impregnation, pyrolysis, and drying the washed AC. The cumulative energy demand of the AC production process from the by-product olive-waste cakes was 167.63 MJ contributed by impregnation, pyrolysis, and drying the washed AC steps. The use of phosphoric acid and electricity in the AC production were the main factors responsible for the majority of the impacts. If certain modifications are incorporated into the AC production, such as implementing synthesis gas recovery and reusing it as an energy source and recovery of phosphoric acid after AC washing, additional savings could be realized, and environmental impacts could be minimized.

Evaluating activated carbon-water sorption coefficients of organic compounds using a linear solvation energy relationship approach and sorbate chemical activities

A linear solvation energy relationship (LSER) approach was used to investigate the evolving contributions of intermolecular interactions controlling organic compound sorption by granular activated carbon (GAC) from water as a function of sorbate chemical activities. Using a particular GAC (20-40 mesh Darco), 14 sorption isotherms were measured using sorbates with diverse functional groups to represent the range of possible surface interactions, and the data for each sorbate were fit with the Freundlich equation. Using interpolated adsorption coefficients, Kd values (L/kg), LSERs for specific sorbate activities (0.1, 0.01, and 0.001 saturation) were deduced. These expressions revealed that the intermolecular interactions controlling sorption to our particular GAC from water evolved with sorbate activities, such that a global correlation dependent on sorbate activity was found: log Kd (L/kg) = [(3.76 +/- 0.28) - (0.20 +/- 0.10) log ai]V + [(-0.80 +/- 0.14) - (0.48 +/- 0.05) log ai]S + [(-4.47 +/- 0.20) + (0.16 +/- 0.06) log ai]B + (0.73 +/- 0.28) - (0.24 +/- 0.09) log ai (N = 176, R2 = 0.96), where log ai is the activity of sorbate i, V is McGowan's characteristic volume for the sorbate, S reflects the compound's polarity/polarizability, and B reflects the compound's electron-donation basicity. Hence, sorption was promoted by dispersive forces and was diminished for sorbates capable of proton acceptance/electron donation, although both of these became less important at higher sorbate activities. Other intermolecular interactions were only weakly contributing (e.g., the "S" term) or were not significant at all for this GAC (i.e., the "R" and "A" terms). This result implies the Freundlich coefficients, Kf, for sorbates are given by (3.76V - 0.80S - 4.47B + 0.73) + (0.20V + 0.48S - 0.16B + 0.24) log Ci,w(satn), and their exponents, 1/n, are equal to -0.20V - 0.48S + 0.16B + 0.76. The data set could also be used to deduce a sorbate concentration-dependent LSER which would be useful for estimating equilibrium sorption coefficients for new sorbates of interest: log Kd (L/kg) = [(1.89 +/- 0.07) - (0.22 +/- 0.06) log Ci,w]V + [(0.90 +/- 0.05) - (0.48 +/- 0.03) log Ci,w]S + [(-2.36 +/- 0.07) + (0.30 +/- 0.05) log Ci,w]B + (2.98 +/- 0.07) - (0.26 +/- 0.06) log Ci,w (N = 176, R2 = 0.98), where log Ci,w is the concentration in water of each sorbate (mg/L).

Life cycle assessment of active and passive groundwater remediation technologies

Groundwater remediation technologies, such as pump-and-treat (PTS) and funnel-and-gate systems (FGS), aim at reducing locally appearing contaminations. Therefore, these methodologies are basically evaluated with respect to their capability to yield local improvements of an environmental situation, commonly neglecting that their application is also associated with secondary impacts. Life cycle assessment (LCA) represents a widely accepted method of assessing the environmental aspects and potential impacts related to a product, process or service. This study presents the set-up of a LCA framework in order to compare the secondary impacts caused by two conceptually different technologies at the site of a former manufactured gas plant in the city of Karlsruhe, Germany. As a FGS is already operating at this site, a hypothetical PTS of the same functionality is adopted. During the LCA, the remediation systems are evaluated by focusing on the main technical elements and their significance with respect to resource depletion and potential adverse effects on ecological quality, as well as on human health. Seven impact categories are distinguished to address a broad spectrum of possible environmental loads. A main point of discussion is the reliability of technical assumptions and performance predictions for the future. It is obvious that a high uncertainty exists when estimating impact specific indicator values over operation times of decades. An uncertainty analysis is conducted to include the imprecision of the underlying emission and consumption data and a scenario analysis is utilised to contrast various possible technological variants. Though the results of the study are highly site-specific, a generalised relative evaluation of potential impacts and their main sources is the principle objective rather than a discussion of the calculated absolute impacts. A crucial finding that can be applied to any other site is the central role of steel, which particularly derogates the valuation of FGS due to the associated emissions that are harmful to human health. In view of that, environmental credits can be achieved by selecting a mineral-based wall instead of sheet piles for the funnel construction and by minimising the steel consumption for the gate construction. Granular activated carbon (GAC) is exclusively considered as the treatment material, both in-situ and on-site. Here it is identified as an additional main determinant of the relative assessment of the technologies since it is continuously consumed.