Resources, Conservation & Recycling 182 (2022) 106313 Contents lists available at ScienceDirect Resources, Conservation & Recycling journal homepage: www.elsevier.com/locate/resconrec Full length article Assessment of the significance of heavy metals, pesticides and other contaminants in recovered products from water resource recovery facilities Natalia Rey-Martínez , Albert Guisasola *, Juan Antonio Baeza GENOCOV. Departament d’Enginyeria Química, Biològica i Ambiental. Escola d’Enginyeria. Universitat Autònoma de Barcelona, Bellaterra, Barcelona 08193, Spain A R T I C L E I N F O A B S T R A C T Keywords: The recovery of valuable materials from municipal water resource recovery facilities (WRRF) is a promising Cellulose option to implement circular economy in wastewater treatment. Different technologies are being evaluated at Heavy metals different WRRF to recover products such as struvite, bioplastics and cellulose. However, the quality of these Resource recovery recovered products remains to be assessed in terms of their possible contamination with various hazardous Wastewater compounds that may compromise their application in agriculture or construction. The aim of this article is Pesticides therefore to assess the quality of products recovered from various recovery techniques implemented at demonstration sites. The results obtained for heavy metals, pesticides, chloroalkanes and PAHs from the analysis of 15 recovered products are reported and compared to the closest regulation framework possible. In general, the results showed that the products met current regulations and only some of them slightly exceeded the limits for very specific pollutants and only for a specific use, such as the food industry. These results are promising to accelerate the market penetration of these recovered products. However, this work highlights the need for a novel regulatory framework for these products that fits with its current uses. 1. Introduction pharmaceuticals, personal care products, endogenous hormones, pesti­ cides and others, which can lead to both health and environmental is­ Resource recovery from municipal wastewater is the starting point sues that restrict its potential use in land application. The maximum for the recent aim of integrating circular economy strategies in the permissible concentration in soil of these toxic elements after applying wastewater sector. This paradigm shift aims at converting wastewater biosolids is regulated by guidelines established, for example, by the treatment plants (WWTPs) into water resource recovery facilities Food and Agriculture Organization (FAO) (Pescod, 1992) and the Eu­ (WRRFs). There are many different methodologies that set the focus on ropean Directive 86/278/EEC (European Commission, 1986). the recovery of materials in WRRFs. Akyol et al. (2020) reviewed the Among these pollutants, the presence of heavy metals is a major recent findings in this field and revealed that some of these technologies obstacle for the land application of sewages sludge derivates due to their are already validated at pilot/full scale and that market niches for long-term accumulation in the soil (Liu and Sun, 2013; Zhang et al., recovered materials are emerging. However, resource recovery still re­ 2017). For instance, the sludge from WRRFs is considered as a secondary quires a legislative framework and technical and socioeconomic as­ P-resource suitable for producing fertilizers, but also as a final fate for sessments to demonstrate that there are no hazards associated with these heavy metals and some other organic contaminants contained in the products and to reveal the market potential of each specific recovered wastewater (Steckenmesser et al., 2018). The associated risks depend on product. several factors including total content, chemical species, and charac­ For example, land application of sewage sludge from WRRFs and its teristics of the soil (Zhang et al., 2017). In a recent review about the derivatives such as biofertilizers is a much more economical and sus­ presence of heavy metals in biosolids for land application, Nunes et al. tainable option than sludge landfill and incineration. However, mate­ (2021) concluded that, despite the numerous advantages of sludge rials derived from sewage and sewage sludge may also contain application (i.e. improving soil chemical characteristics, hazardous materials, including heavy metals, polychlorinated n-alkanes, agricultural-morphological features and crop yields in various species), polycyclic aromatic hydrocarbons (PAHs), detergent residues, an adequate heavy metal screening is necessary. Most of the results * Corresponding author. E-mail addresses: natalia.reymartinez@gmail.com (N. Rey-Martínez), Albert.Guisasola@uab.cat (A. Guisasola), JuanAntonio.Baeza@uab.cat (J.A. Baeza). https://doi.org/10.1016/j.resconrec.2022.106313 Received 1 December 2021; Received in revised form 2 March 2022; Accepted 21 March 2022 Available online 4 April 2022 0921-3449/© 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by- nc/4.0/). N. Rey-Martínez et al. Resources, Conservation & Recycling 182 (2022) 106313 presented were within legal limits; however, some crop products impurities in water, air and food products. EU regulation 1272/2013 showed values of concern for human food consumption in developing (European Commission, 2013) sets limits for eight PAHs classified as countries. Therefore, strict guidelines with adequate regulatory over­ priority for rubber and plastic materials of toys/childcare articles (0.5 sight are required to control contamination by heavy metals of agri­ mg kg− 1), and for all other consumer materials in contact with skin (1 cultural soils. Composting and chemical immobilization have been mg kg− 1) (European Commission et al., 2018). proposed to minimize these problems and to effectively bind heavy The SMART-Plant project (SMART-Plant, 2021a) has recently re­ metals to sewage sludge. Smith (2009) reviewed the heavy metal con­ ported the performance of innovative processes implemented in WRRFs tent of compost when compared to the municipal waste solids and at a relevant demo-scale (technological readiness level, TRL = 6–7) to showed that the former contained more heavy metals than those present harvest valuable substances such as cellulose fibers (Palmieri et al., in the soil. They observed that the compost from 2019; Zhou et al., 2019), bioplastics as polyhydroxyalkanoates (PHAs) mechanically-segregated municipal solid waste generally contained a (Conca et al., 2020; Lorini et al., 2021; Palmieri et al., 2021) and nu­ higher heavy metal concentration than that from source-segregated. trients as fertilizers (Guerra et al., 2019; Guida et al., 2020; Larriba et al., Alternatively, thermochemical treatments have also been proposed to 2020) (Fig. 1). The objective of this work was to evaluate the quality of remove heavy metals and significantly reduce their bioavailability and these products as materials that could potentially be applied in agri­ plant uptake (Steckenmesser et al., 2018). culture or construction. To this aim, samples of these recovered products Pesticides are other relevant group of compounds that can be were dried or lyophilized, then homogenized and finally they were potentially harmful. A pesticide controls potential diseases or damaging analyzed for heavy metals (Cd, Cr, Cu, Hg, Mg, Ni, Pb and Zn), pesticides organisms in plants and/or plant products during the whole process of (108 compounds), chloroalkanes (C10–13) and PAHs (16 compounds). production, storage and transport. Thus, pesticides contain active sub­ This work does not focus on the different technologies developed to stances (plant extract, microorganism, pheromone or chemical) that can obtain these products, which are already explained by the respective disturb the existing microbiota or lead to environmental or health issues research groups that have developed them, but on whether the 15 when applied to the soil. Pesticides are extensively used due to the ad­ products that were recovered complied with the corresponding legisla­ vantages of increased productivity and controlling vector diseases, but tion. In many cases, no legislation was detected to provide guidance on exposure to them is extremely destructive for human health, flora, fauna the suitability of these products, so the results are compared with each and the environment (Rani et al., 2021). Moreover, they can accumulate other and with the most related legislation and works that could be in groundwater and have persistent effects even after being banned found. The comparison with legislation and previous results is really (Sackaria and Elango, 2020). For these reasons, the presence and con­ important to evaluate the results obtained, since without a proper sequences of pesticides is a very important area of research as the framework it is not possible to decide whether the concentrations number of publications is yearly increasing: around 72,000 research detected are significant or not. The problem of the lack of legislation is a documents were published and reported in the PubMed database be­ real limitation to regulate the use of these products, and is one of the tween 2011 and 2020 (Rani et al., 2021). most important practical problems when trying to apply the results of Chloroalkanes C10–13 are short chain chlorinated paraffins (SCCPs) the resource recovery projects in real life. that are classified as dangerous substances (European Commission, 1967), since they are considered to be carcinogenic and can lead to 2. Materials and methods long-term harmful impacts in the aquatic environment. These com­ pounds are not significantly biodegradable, and they can be adsorbed 2.1. Evaluated samples onto the sludge. Hence, the application of sewage sludge that contains SCCPs can result in its migration to surface water (European Commis­ Different types of samples from the different resource recovery sion, 2000a). Among the chlorinated parafilm substances, SCCPs have technologies were analyzed in this study: PHA-enriched sludge, recov­ the highest transport potential, bioaccumulation and toxicity, but ered PHAs, cellulose and biocomposite enriched in cellulose or PHAs further studies are needed to understand the extent of their potential (Table 1). These products were obtained in some of the smart technol­ harmful effects (POPRC, 2015; van Mourik et al., 2016). There is ogies (Smartechs) demonstrated at relevant pilot scale in the SMART- currently sufficient data available to conclude that SCCPs meet the Plant project (SMART-Plant, 2021a). Table 1 provides a brief descrip­ UNEP Stockholm Convention criteria to be designated as a persistent tion of each sample, its potential use, the technology used to produce it organic pollutant. and the available references describing the Smartechs. The description Finally, polycyclic aromatic hydrocarbons (PAHs) are among the of the Smartechs can also be found in the technical factsheets developed most prevalent organic pollutants in contaminated land and have a for the project that are included as supplementary information (SI) carcinogenic potential and a high persistence. Thus, PAHs presence can (SMART-Plant, 2021b). result in severe health risks (Khillare et al., 2020). PAHs appear natu­ Samples 1, 2, 4, 5 and 6 were homogenized by crushing in a mortar rally in crude oil, gasoline and coal, but they also are generated during and sieved to 0.5 mm. Samples 3, 7, 8, 9, 10 and 11 were frozen at − 50 the inefficient combustion of organic materials such as garbage, tobacco, ◦ C and then lyophilized for 48 h, homogenized by crushing in a mortar, gas, oil, coal and wood. The potential presence of PAHs in soils has sieved to 0.5 mm and stored at − 20 ◦ C until analysis. Samples 12, 13, 14 increased due the recent utilization of combustion, pyrolysis, and gasi­ and 15 are board-shaped composites and they were cut and milled, then fication for sludge treatment (Dai et al., 2014; Ko et al., 2018; Kończak homogenized by crushing in a mortar and sieved to 0.5 mm. Finally, all et al., 2019; Liu et al., 2021; Park et al., 2009). PAHs can naturally be samples were analyzed externally by certified laboratories. biologically degraded or removed through soil erosion or volatilisation. However, an excessive amount can lead to its adsorption in crops and, in 2.2. Pesticides the end, become a hazard to health. PAHs have a wide range of half-life values (from days to several years) depending on compound and the The concentration of more than one hundred pesticides (108) was environmental conditions (Saveyn and Eder, 2014). PAHs are more measured (Table S1 in SI) by Soluciones Analíticas Instrumentales present in sewage sludge than other common pollutants such as halo­ (Sailab) (Cerdanyola del Vallès, Catalonia). The pesticides were genated hydrocarbons, nitroaromatics, chlorobenzenes, and haloethers extracted using a commercial salt packet of QuEChERS (Quick, Easy, (Cai et al., 2007; Sun et al., 2019; Joint Research Centre et al., 2013). Cheap, Effective, Rugged and Safe) with the methodology reported in Therefore, the land application of a PAH-contaminated sludge may pose the SI. Then, it was conducted a clean-up step with primary-secondary a serious risk on health (Bandowe et al., 2014; Shrivastava et al., 2017; amine (PSA) and C18. Finally, the extract was diluted with water (1:2) Sun et al., 2019). Thus, EU regulation limits their presence as undesired and analyzed with GC/MS/MS by a proprietary method developed by 2 N. Rey-Martínez et al. Resources, Conservation & Recycling 182 (2022) 106313 Fig. 1. Scheme of the SMART-Plant project and some of the recovered products analyzed in this work. Sailab. The limit of quantification (LOQ) for pesticides was 0.010 mg (ICP-MS) spectrometry (Model 7500ce, Agilent Technologies). The kg− 1. analysis for mercury (Hg) were made with 50 mg of sample, without any previous treatment. The content of Hg was determined by thermal 2.3. Polycyclic aromatic hydrocarbons (PAHs) decomposition followed by atomic absorption spectrophotometry (DMA-80, Milestone). PAHs were analyzed by Sailab. 16 PAHs were analyzed (Table S2) by GC/MS/MS after using the same extraction performed for pesticides. 2.6. Risk assessment The LOQ for PAH was 0.010 mg kg− 1. The safety related to the use of the SMART-products depends on the destination of the product. The highest risk is associated with the use of 2.4. Chloroalkanes sludges and related materials as fertilizers. To allow a safe use of these products, a guideline on maximum amounts which can be used annually, SCCPs (chloroalkanes C10–13) were also analyzed by Sailab. SCCPs without generating an ecotoxicological risk, is needed. This evaluation between 10 and 13 carbons were extracted with hexane and measured can be performed by considering the following values: i) the predicted with a GC/MS/MS proprietary method developed by Sailab based on a no effect concentration (PNEC) values, ii) the specific maximal biolog­ methodology proposed by Zencak et al. (2004). LOQ for chloroalkanes ical half-life and iii) the maximum annual pollutant input per hectare was 0.010 mg kg− 1. (ha) of agricultural land that has no negative effect on the ecosystem (based on the technical guidance document by European Commission on 2.5. Heavy metals risk assessment EU-TGD (European Commission, 2003a)). The PNEC values are provided for groundwater organisms and, therefore, by The hHeavy metals analyses were conducted by the Chemical accepting them, we are assuming as a rough estimate that soil organisms Analysis Service of the UAB. The samples (0.25 - 0.5 g) were digested (in are equally or less affected by these pollutants. The acceptable fertilizer triplicate) with concentrated HNO3 (Merck) in a microwave digester application (i.e. the maximum amount of sample that can be used as (Ultrawave, Milestone). The digested samples were diluted with HNO3 fertilizer per year) can be calculated as Eq. (1): 1% (v/v). Cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) were analyzed by inductively coupled plasma mass 3 N. Rey-Martínez et al. Resources, Conservation & Recycling 182 (2022) 106313 Table 1 Identification and description of the samples evaluated. Sample Description Potential use SMART-Plant identity and references 1 Solid dry cellulose recovered as primary treatment of municipal Raw material for bio-composites SMARTech1 (Palmieri et al., 2019; Zhou wastewater–light-weight structural material, hygienically safe (EPA class A), (samples 12 and 15) and other et al., 2019) with an acceptable odor after specific treatment with perfume essences and with buildings materials an organic residue < 10%. The demo plant was located in Carbonera (Italia) 2 PHA extracted from PHA-rich biomass (sample 3). Powder with PHA content > Suitable for bio-composite production SMARTech5 (Conca et al., 2020; Lorini 95%. High quality due to the ratio HB:HV = 60:40 or bioplastic input for low-grade et al., 2021; Palmieri et al., 2021) applications 3 PHA-rich biomass–PHA-rich organic material with a PHA content up to 30–40% Bio-based ingredient for bio- SMARTech5 (Conca et al., 2020) of dry matter obtained from a side-stream SBR using volatile fatty acids from composites (sample 13) fermentation of cellulosic primary sludge. This demo plant was also located in Carbonera (Italia) 4, 5 and Three batches of N and P salts recovered from WWTP effluents by ion-exchange Use as a feedstock in fertilizer industry SMARTech3 (Guida et al., 2020; Huang 6 processes (calcium phosphate and ammonium phosphate). Hybrid anion et al., 2020) exchangers (HAIX) were used for P recovery and zeolite and mesolite for N recovery. The samples were obtained during different periods of operation. The demo plant was located in Cranfield University (UK) and treated municipal wastewater after secondary treatment with trickling filters removing organic matter. 7 Struvite (MgNH4PO4⋅6H2O) recovered from an EBPR-based two-sludge system Use as a feedstock in fertilizer industry SMARTech2b (Larriba et al., 2020) for the treatment of urban wastewater in Manresa (Spain) 8 Struvite produced by SCEPPHAR Carbonera (a side-stream EBPR system), solid Use for land application SMARTech5 (Conca et al., 2020) phosphate soft mineral (Mohs hardness of 1.5–2) 9 Excess P-rich sludge produced by the side-stream system SCENA for via-nitrite N Use for land application SMARTech4a removal in Carbonera 10 Compost generated from P-rich sludge for its direct and safe use in agriculture. Bio-based fertilizer and nutrient rich SMARTechDownstreamB (Guerra et al., The demo plant was located in Manresa (Spain) stabilised organic amendment 2019) 11 Excess sludge produced from a side-stream SCENA-Thermal Hydrolysis process. Bio-based fertilizer and nutrient rich SMARTech4b The demo plant was located in the Psyttalia WWTP in Athens (Greece). stabilised organic amendment 12 and Bio-composite produced with cellulose (12) or PHA (13)–It possesses high water Bio-composite for outdoor use, SMARTechDownstreamA (Zhou et al., 13 resistance and stability and low potential for slip suitable for benches, fences and 2019) decking 14 and WPC (wood plastic composite) and SPC (wood-recovered cellulose composite). Building materials for outdoor use SMARTechDownstreamA (Zhou et al., 15 SPC contains up to 40% of recovered sludge cellulose 2019) ( ) ( ) LowRiskInput mg⋅(ha⋅a)− 1 Acceptable fertilizer application kg⋅(ha⋅a)− 1 = C (mg⋅kg− 1 ) (1) where the LowRiskInput is the yearly input to cropland that presents a low risk and C is the concentration in the solid sample. 3. Results and discussion 3.1. Pesticides To the best of our knowledge, there is no specific regulation for pesticide concentration in recovered products from wastewater treat­ ment as there is in other sectors (e.g. biosolids). For example, the approved/non-approved pesticides in the food industry are classified according to a maximum residue limit (MRL) for each type of product (fruits, vegetables, cereals, spices, etc.). MRL is the maximum concen­ tration of a pesticide legally accepted in food or animal feed (Pescod, 1992). If the chemical content of a certain compound exceeds the MRL, the marketing of the product shall cease and the cause of contamination shall be investigated. Due to the lack of specific regulation, we compared the concentration values found in our recovered products with the MRL values reported for different types of food. Despite this difference, we used this conservative approach since some of bio-recovered products could be used as fertil­ ization products and somehow enter the food chain. Thus, estimating the potential migration of pesticides from the recovered material to food chains is essential to ascertain the use of these materials as fertilizers. The food-related MRLs are the most restrictive and the MRLs in non- edible materials should be much higher than those (Table 2). For ease of comparison, Table 2 only provides the highest and the lowest MRLs of those found in the regulation. Six pesticides classified as active substances in the EU pesticides 4 N. Rey-Martínez et al. Resources, Conservation & Recycling 182 (2022) 106313 Table 2 sample. This value should be considered as a conservative top limit for Detected pesticides in samples 5 and 8 compared to their MRLs for food. The cropland application. High tolerable fertilizer application levels were concentration of pesticides in the rest of samples analyzed was below the obtained for cyprodinil and terbutryn indicating that these substances detection limit. should not be a problem for the application of the products from Pesticide Sample 5 Sample 8 Regulation (EC) MRL* resource recovery. Nevertheless, for cyhalothrin, the very low PNEC and (mg⋅kg− 1) No 1107/2009 (mg⋅kg− 1) relatively high half-life leads to a low acceptable input. Hence, this Bifenthrin 0.018
270000 5 L-Cyhalothrin 2.2 10− 200 2 29 Terbutryn 0.065 300 ≥ 6000 > 38700 a Source for PNECs (chronic): (Ecotox Centre Switzerland, 2020). b The “worst-case” scenario based on similar chemicals has been assumed for non-available data. c To agricultural land. Table 4 1 Average values of PAHs detected (mg kg− of dry matter). No PAHs were detected in the other samples. Sample 3 5 8 9 11 PAHs Sum 0.030 ± 0.021 0.622 ± 0.721 0.229 ± 0.214 0.034 ± 0.012 0.016 ± 0.011 Anthracene 0.034 ± 0.024 0.131 ± 0.169 Benzo(b)fluoranthene 0.043 ± 0.030