Sewage Sludge Soil Research Articles

Ecological risk assessment of heavy metals from application of sewage sludge on agricultural soils in Europe

AbstractThe present European Union (EU) Sewage Sludge Directive (86/278/EEC) is undergoing modifications aimed at enhancing its applicability in the agricultural sector. The Directive's existing limit values for heavy metal concentrations in soils are in the process of being revised. However, to comprehensively understand their effects on EU agricultural lands, additional evaluations are necessary. This is particularly important given that ecological risk assessments are often performed on a site‐specific basis, potentially overlooking broader regional implications. The main objective of the current work is to introduce a methodological approach to quantify the impact of sewage sludge (SS) application on agricultural soils in the EU and the United Kingdom. Concentrations of heavy metals (HMs) (Cd, Cu, Hg, Ni, Pb and Zn) in agricultural land from Land Use/Land Cover Area Frame Survey (LUCAS) 2009 topsoil database were used as a baseline. Maximum quantities of SS that can be safely applied to agricultural lands were obtained by a modeling procedure was used to determine the maximum safe quantities of SS that can be applied to agricultural lands for each country within the European Member States and the United Kingdom. Accumulation of HMs in soils was modelled by using a representative SS composition, distributed over 10 successive years at 5 Mg ha−1 year−1 rate. Ecological risk impact was assessed by using both the single ecological risk index (Er) and the integrated potential ecological risk index (RI). Maximum quantities of SS applied on agricultural soils in EU + UK were estimated to be 45 Mg ha−1 at the country level. We found that 19% of agricultural land (around 28,471,900 ha) in the EU + UK shows a higher RI than moderate risk after long time application of the representative SS. We show that the combination of the HM concentrations from the LUCAS topsoil survey and assumptions on the SS composition and soil HM partitioning can be used to define the actual and potential soil pollution rate in EU + UK. We demonstrate that the proposed methodology can be used by policymakers, farmers, regional authorities and other stakeholders, with possible adaptions based on local in‐depth soil and SS knowledge.

Effect of biological sewage sludge and its derived biochar on accumulation of potentially toxic elements by corn (Zea mays L.)

The land application of sewage sludge can cause different environmental problems due to the high content of potentially toxic elements (PTEs). The objective of this study was to compare the effect of urban biological sewage sludge (i.e. the waste of activated sludge process) and its derived biochar as the soil amendments on the bioavailability of PTEs and their bioaccumulation by corn (Zea mays L.) under two months of greenhouse conditions. The soil was treated by adding biochar samples at 0 (control), 1, 3, 5% w/w. The diethylenetriamine pentaacetic acid (DTPA)-extractable concentrations of PTEs including Zn, Pb, Cd, Cr, Ni, Fe, and Cu in soil and their accumulation by plant shoot and root were measured. Conversion of the biological sewage sludge into the biochar led to decrease the PTEs bioavailability and consequently decreased their contents in plant tissues. The DTPA extractable metal concentrations of produced biochar in comparison to the biological sewage sludge reduced 75% (Cd), 65% (Cr), 79% (Ni and Pb), 76% (Zn), 91% (Cu) and 88% (Fe). Therefore, the content of Ni, Fe, Zn and Cd in corn shoot was decreased 61, 32, 18 and 17% respectively in application of 5% biochar than of raw sewage sludge. Furthermore, the application of 5% biochar enhanced the physiological parameters of the plants including shoot dry weight (twice) and wet weight (2.25 times), stem diameter (1.70 times), chlorophyll content (1.03 times) in comparison to using 5% raw sewage sludge. The results of the study highlight that application of the biochar derived from urban biological sewage sludge in soil could decrease the risk of PTEs to the plant.

Sewage sludge amendment of rice as a potential alternative to mineral fertilizer: Analyses of physiological, biochemical and molecular mechanisms of plant response

Sewage sludge (SS) disposal poses environmental concerns, yet its organic matter, macro- and micronutrients, make it potentially beneficial for enhancing soil quality and crop yield. This study focuses on three types of SS: “R10” (SS1), which is commonly used in agricultural practices, and two environmentally friendlier options (SS2 and SS3), as alternatives to mineral fertilizer (urea) for rice cultivation. A pot experiment was conducted to investigate the ecophysiological, biochemical, and molecular responses of rice at three different growth stages. SS application led to a significant increase in biomass production (particularly SS3), along with increased nitrogen (N) levels. Enhanced chlorophyll content was observed in SS-treated plants, especially during inflorescence emergence (with the highest content in SS3 plants). At the ecophysiological and biochemical levels, SS treatments did not adversely affect plant health, as evidenced by unchanged values of maximal PSII photochemical efficiency and malondialdehyde by-products. At biochemical and gene expression levels, antioxidant enzyme activities showed transient variations, likely related to physiological adjustments rather than oxidative stress. Ascorbic acid and glutathione did not significantly vary. This study concludes that the use of SS in soil can be a viable alternative fertilizer for rice plants, with positive effects on biomass, chlorophyll content, and no adverse effects on plant health. Among the tested SSs, SS3 showed the most positive effect, even compared to commercial fertilizer. These results suggest that SS application could improve rice yield while addressing environmental concerns surrounding SS disposal.

Differential impacts of sewage sludge and biochar on phosphorus-related processes: An imaging study of the rhizosphere

Recycling of phosphorus (P) from waste streams in agriculture is essential to reduce the negative environmental effects of surplus P and the unsustainable mining of geological P resources. Sewage sludge (SS) is an important P source; however, several issues are associated with the handling and application of SS in agriculture. Thus, post-treatments such as pyrolysis of SS into biochar (BC) could address some of these issues. Here we elucidate how patches of SS in soil interact with the living roots of wheat and affect important P-related rhizosphere processes compared to their BC counterparts. Wheat plants were grown in rhizoboxes with sandy loam soil, and 1 cm Ø patches with either SS or BC placed 10 cm below the seed. A negative control (CK) was included. Planar optode pH sensors were used to visualize spatiotemporal pH changes during 40 days of plant growth, diffusive gradients in thin films (DGT) were applied to map labile P, and zymography was used to visualize the spatial distribution of acid (ACP) and alkaline (ALP) phosphatase activity. In addition, bulk soil measurements of available P, pH, and ACP activity were conducted. Finally, the relative abundance of bacterial P-cycling genes (phoD, phoX, phnK) was determined in the patch area rhizosphere. Labile P was only observed in the area of the SS patches, and SS further triggered root proliferation and increased the activity of ACP and ALP in interaction with the roots. In contrast, BC seemed to be inert, had no visible effect on root growth, and even reduced ACP and ALP activity in the patch area. Furthermore, there was a lower relative abundance of phoD and phnK genes in the BC rhizosphere compared to the CK. Hence, optimization of BC properties is needed to increase the short-term efficiency of BC from SS as a P fertilizer.

Grain and Foliar Nutritional Responses of Corn (Zea mays L.) to Sewage Sludge Soil Application

Grain and Foliar Nutritional Responses of Corn (Zea mays L.) to Sewage Sludge Soil Application

Strength Behaviour of Sugarcane Bagasse Ash Treated Sewage Sludge-Soil Mixture

Laboratory tests were conducted on sugarcane bagasse ash treated sewage sludge-soil mixture with 5%, 10% and 30% bagasse ash to assess its strength behaviour. Unconfined compressive strength (UCS) was performed to observed influence of bagasse ash content (BAC), curing time, water content on value of UCS and axial strain. Soil sample were prepared using standard proctor at 60% of optimum water content. Results recorded value of UCS reached peaked at 20% BAC and then dropped by 46% at 30% BAC. Axial strain increased for every additional BAC. Result shown curing period influence UCS, as curing time longer the value of UCS also rose. Other findings of this study were BAC affected maximum dry density (MDD), 5% BAC and 10% BAC improved MDD but 20% BAC and 30% BAC would reduce value UCS. Finally, it could be concluded 20% BAC was the optimum content to get the optimal UCS improvement of sewage sludge-soil.

The Usefulness of Ozone-Stabilized Municipal Sewage Sludge for Fertilization of Maize (Zea mays L.)

Sewage sludge generated in the wastewater treatment process is a waste material and a serious environmental nuisance. Due to its specific properties, the management and final disposal of sewage sludge is a considerable problem also in Poland. Ozonation of sewage sludge is the most commonly used process based on the use of oxidizing agents for stabilization of the waste. This process results in substantial reduction of the sludge volume and simultaneous production of small amounts of toxic by-products. Despite the effectiveness of ozone in sanitation and reduction of sludge amounts and in improvement of many parameters, still little is known about the use of ozonated sewage sludge for agricultural purposes, e.g., fertilization of arable crops. Therefore, the present study was an attempt to evaluate the effect of ozone-stabilized sewage sludge on maize development in initial stages of growth in pot experiment conditions. We analyzed the effect of ozone-stabilized sewage sludge in soil on dry matter yields of aboveground parts of maize. We also conducted physiological measurements of chlorophyll content, fluorescence, and exchange. Additionally, the content of macro- and microelements and toxic heavy metals in aboveground maize biomass was determined. The ozone-stabilized sewage sludge exerted a positive impact on all maize parameters in the initial stage of growth. Compared to the control, plants fertilized with this type of sludge were characterized by a 50% higher yield of aboveground biomass and over 80% higher content of chlorophyll. Furthermore, the content of most macro- and microelements in the aboveground biomass was generally higher in plants fertilized with the ozonated sludge than in plants from the other experimental variants. The chlorophyll fluorescence and gas exchange parameters in plants fertilized with ozonated sludge were improved. No excessive accumulation of Pb and Cd was detected. The present results have confirmed that ozone-stabilized sewage sludge can be used for cultivation of agricultural plants, as it improves utilization of deposited nutrients. The improved bioavailability of nutrients was associated with ozonation-induced initial degradation of organic matter and release of deposited plant nutrients.

Planned Application of Sewage Sludge Recirculates Nutrients to Agricultural Soil and Improves Growth of Okra (Abelmoschus esculentus (L.) Moench) Plants

The aim of this study was to investigate the feasibility of using sewage sludge (SS) biosolids as a low-cost soil fertilizer to improve soil characteristics and crop yields. Okra (Abelmoschus esculentus (L.) Moench) plants were grown in soil supplemented with different concentrations of SS (0, 10, 20, 30, 40, and 50 g/kg). The results showed that SS soil application led to improved soil quality with a 93% increase of organic matter (at SS dose of 10 g/kg), decreased pH (a reduction from 8.38 to 7.34), and enhanced macro- and micro- nutrient contents. The levels of all the investigated heavy metals (HMs; Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) in the postharvest SS-amended soil were within the prescribed safe limits. The application of SS to soil considerably enhanced the growth parameters of okra plants. Total biomass increased 13-fold and absolute growth rate increased 10-fold compared to plants grown in nonamended (control) soils. Among the applied SS doses, the 10 g/kg SS dose led to the highest values of the measured growth parameters, compared to those of plants grown in control soils. The induced growth at 10 g/kg SS was accompanied by a substantial increase in metal content in roots, stems, leaves, and fruits; however, all levels remained within safe limits. Consequently, the data presented in this study suggest that SS could be used as a sustainable organic fertilizer, also serving as an ecofriendly method of SS recycling.

Part A: Sanitization and use of sewage sludge in soil Technical Note 2 - Legislation aspects

The use of sewage sludge in soil is a environmentally sustainable practice, compatible with the Brazilian Policy of Solid Wastes. Due to its content of organic compounds and nutrients, the sludge is beneficial to the physical, chemical and biological soil properties and to the development of plants. However, since it may contain chemical and microbiological pollutants, it has to be carefully used by following criteria and procedures concerning the protection of the environment and public health. In 2020, Brazil approved Resolution 498 of CONAMA for the definition of criteria and procedures for production and application of biosolids in soil. Besides its agricultural use, this Resolution covers other uses, such as the recuperation of degraded areas. For the use of sludge on land, it needs to be processed in a Sludge Management Unit licensed by a local environmental agency. Depending on the criteria in the Resolution, biosolids are classified under Classes A and B for their microbiological quality, and under Classes 1 and 2 for their chemical aspects.

Part A: Sanitization and use of sewage sludge in soil Technical Note 1 – Topics of interest

Sewage treatment plants (STPs) generate solid by-products that need to be managed safely so as not to compromise the environment and public health. Among these by-products, of special interest is the sludge generated in the primary, biological and physical-chemical treatment units, which concentrates a large amount of the pollutants and contaminants removed during sewage treatment. However, the sludge is also a reservoir of compounds that can be recovered or reused (e.g.: organic matter, phosphorus, and nitrogen), which are of agronomic interest and can be used for the recovery of degraded areas. This technical note (TN), the first of the collection “Valorization and management of solid by-products of sewage treatment. Part A: Sanitization and use of sewage sludge in soil”, presents topics of interest related to modern management of the sludge generated in STPs, with emphasis on the legal aspects and forms of treatment for its transformation into biosolid for use in soils and other possibilities. The other TNs that are part of this collection deepen the topics briefly addressed in this first TN.

Part A: Sanitization and use of sewage sludge in soil Technical Note 4 - Sludge sanitization by alkaline stabilization

Alkaline stabilization (AS) is one of the most widespread processes in the world for the sanitization of sludge produced in sewage treatment, although in Brazil it is used by only a few sanitation companies. The fact that an environmentally sustainable destination for sewage sludge is not mandatory, as well as a series of economic, technical and operational factors, end up limiting the AS process application. The increase of AS practices are expected due to the the Brazilian CONAMA Resolution nº 498/2020, which aims to increase the use of biosolids in agriculture and to further deepen technical and operational knowledge related to this practice. This technical note (TN) presents the main forms of the storage and application of lime, as well as the minimum parameters required for designing maturation and curing yards. In this TN, the intrinsic AS costs and best engineering practices used are discussed, in view of reducing possible problems and maximizing its usage throughout the national territory.

Part A: Sanitization and use of sewage sludge in soil Technical Note 7 - Use of biosolids to recover degraded areas

Organic matter (OM) is fundamental in the rrecovery of degraded areas (RDA), particularly when concerning the soils’ chemical and physical properties. The biosolid obtained from sewage sludge is an important source of OM and nutrients. This technical note discusses the influence of both on RDA, as well as the potential for using biosolids for that purpose. OM acts as a reservoir of nutrients, which are gradually released; it improves the cation exchange capacity of the soil; and it can complex or chelate metals potentially toxic to plants. It is also highlighted its influence on the reduction of the specific mass of the soil, the formation of micro and macro aggregates, the improvement of soil stability, and the increase of soil specific surface. The practical aspects of biosolids use in RDA are discussed in the light of CONAMA Resolution 498/2020, mainly about the criteria for calculating the application doses. Two case studies are also presented.

Experience of using sewage sludge in soil for green building

Wastewater sludge from municipal wastewater treatment plants in Nizhny Novgorod and soils based on them, prepared with different ratios of sludge, sawdust and peat, have been investigated. Sewage sludge-based soils contain plant nutrients and are suitable for use as fertilizing materials in green building. Under the conditions of a three-year lysimetric experiment on cereal lawn grasses, a significant efficiency of organic soils was noted in comparison with traditional soils. The lawn maintenance regime revealed differences in the mixtures of fertilizing materials in terms of the effect on the productivity of the phytocenosis. Use of sewage sludge containing large amounts of heavy metals as one of the soil components undoubtedly leads to increase in the amount of these toxic elements in the soil as a whole.

Part A: Sanitization and use of sewage sludge in soil Technical Note 3 - Sludge sanitization by composting

The final disposal of sludge is one of the major drawbacks in the management of sewage treatment because of its production and accumulation, demanding systematic discharge. Landfilling, sludge-toenergy recovery methods and agricultural use are some alternatives of final destinations. For agricultural purposes, the sludge should undergo an sanitization. Composting can be used for sanitization and the resulting compost contains stabilized organic matter and nutrients that are useful for plants and soil conditioning. This Technical Note (TN) was prepared by consolidating knowledge of researchers and practical specialists, as well as information from specialized literature. Basic concepts, design criteria and operational techniques were sought with the aim of enabling sewage sludge transformation via composting, not only to produce a quality product, such as fertilizer, but also to benefit the environment.

Part A: Sanitization and use of sewage sludge in soil Technical Note 6 - Agricultural use of biosolids

The biosolids resulting from the sludge treatment from sewage treatment plants improve soil conditioning and are rich in nutrients. However, despite the benefits to soil and plants, as well as the sustainable appeal, the agricultural use of biosolids in Brazil is still not widespread. In this Technical Note (TN), the objective is to present some Brazilian experiences with biosolids in the light of relevant legislation, as well as to discuss aspects and potential related uses. Paraná and São Paulo states are the main references in agricultural use, with experiences of sanitization with alkaline stabilization and composting. In this TN the criteria for the use of biosolids are presented, according to the new CONAMA Resolution 498/2020, as well as the challenges related to the agricultural sector and public acceptance. Public policies to support rural producers for the application of biosolids are also discussed, to promote transformation of a rich by-product of sewage treatment into a resource for agricultural use, in a vision of circular economy.

Part A: Sanitization and use of sewage sludge in soil Technical Note 5 - Thermal sludge drying and sanitization

Thermal drying of the sludge produced in sewage treatment plants (STPs) is a physical process that allows for a significant reduction of the moisture intrinsic to the material, reducing its mass and volume for handling and final disposal. The process also allows for thermal sanitization of the sludge, dispensing the use of chemical products for that purpose. A fundamental requirement for the operationalization of the process is the availability of heat, which can be obtained, for example, through the energy recovery of biogas and the dry sludge found in STPs, corroborating with the concepts of sustainability, renewable energy and circular economy. Although thermal sludge drying is already consolidated in several countries, it is still not a common practice in Brazil. Therefore, this technical note presents the main topics of interest associated with drying and thermal sanitation of sludge for STPs of different sizes, as well as a review of the fundamentals inherent to the process and the methods for selection of dryers. This document also reports examples of thermal sludge drying and sanitization systems, in addition to important aspects to be considered when implementing the process in STPs.

Evaluation of Land Potential for Use of Biosolids in the Coastal Mediterranean Karst Region

The aim of this study was to evaluate the potential of agricultural land in the coastal Adriatic Karst region (Šibenik region, Croatia) for biosolids application by integrating spatial data from different sources: digital maps and remote sensing, parcel identification system, GIS field observations and measurements focusing on specific land and soil properties. Due to the rapid development of the wastewater treatment industry, excessive accumulation of sewage sludge (SS) in wastewater treatment plants is a growing problem worldwide. Management options for land application of biosolids require a comprehensive characterization of both SS and SS-amended soils. The assessment of agricultural land in the study area for SS disposal was based on EU and national legislation. The evaluation revealed that agricultural land in the study area accounts for only 10% of the total area (25,736 ha), but only a quarter of the existing land (6065 ha) is suitable for biosolids application. Furthermore, the data indicate that the sewage sludge can be safely applied to the soil in terms of soil metals according to the Croatian legislation. The short-term potential of the soil to sustain this ecosystem service, namely soil improvement with biosolids, should be used to determine the inherent long-term potential based on resistance to soil degradation and resilience. However, caution is needed and the long-term effects should be investigated before biosolids are continuously used for soil application.

Sorption of Heavy Metals by Sewage Sludge and Its Mixtures with Soil from Wastewater Treatment Plants Operating in MBR and INR Technology.

Sewage sludge is a very complex system, with solids and water. It is generated as waste from wastewater treatment. Sewage sludge is used to fertilize agricultural and forest areas and to rehabilitate devastated areas. It is a good organic fertilizer because it contains significant amounts of nutrients beneficial for plant development and humus-forming substances. The composition of sludge from municipal wastewater treatment plants is similar to soil organic matter, therefore it can be used to improve the physicochemical properties of soil, increasing its sorption capacity. Research material was collected in the Swietokrzyskie and Mazowieckie Voivodships. Sewage sludge was collected from the wastewater treatment plants in Sitkowka Nowiny (Sitkowka) and Kunow, as well as high-quality agricultural soil from Opatowiec and sandy-clay soil from Jastrzebie. Research was carried out on the sorption of heavy metals (Cd, Cr, Cu, Pb, Ni, Zn) by mixtures of sewage sludge with soil. The calculations were made for the concentrations of heavy metals in sewage sludge, soil, and sewage sludge–soil mixtures. The geoaccumulation index (Igeo) and the risk assessment code (RAC) were calculated. Increased sorption capacity was demonstrated in samples with a predominance of sewage sludge. It was shown that heavy metals from sewage sludge, after mixing with soil, changed their form from immobile to mobile.

Characterization of organic compounds and drugs in sewage sludge aiming for agricultural recycling

The application of sewage sludge in soils can bring benefits to agricultural productivity, however, the risks arising from this application must be measured and carefully evaluated. Persistent organics compounds and drugs can be present in the sewage sludge and if applied to the soil, they can cause severe risks to the soil biota and contamination of groundwater. This work determined 174 persistent organic compounds and drugs in sludge samples from a wastewater treatment plant using chromatographic methods. The drugs ciprofloxacin, enrofloxacin and diclofenac were quantified, and values varied according to sampling period. For persistent organic compounds, cresols were the most abundant compounds in sewage sludge. With the analyses made of both the elutriate and the filtrate, it was possible to verify the potential for soil retention or leaching that each compound can present with the application of sewage sludge in the agriculture.

Evaluating the Effect of Sewage Sludge on Bioactive Components of Momordicacharantia

Momordicacharantia L. belongs to the family Cucurbitaceae. This plant has widely been reported for use in traditional medical systems for the treatment of diabetes, rheumatism, intestinal gas and malaria. The ethnicity of M. charantiais Asia, Africa and some parts of Europe where it is considered edible. Sewage sludge, a by-product of waste water treatment plant, contains several nutrients. These nutrients are known as beneficial for the better growth and good yield of the plants. The objective of this study is to optimize soil with different ratios of sewage sludge for increased growth of bioactive components in M. charantia. The plant was grown at six places; in soil containing 20%, 40%, 60% and 80% sewage sludge ratio as well as in pure soil and in pure sewage sludge. Fruit harvesting was carried out after 75 days. Methanol extract of M. charantia (Fruit) was subjected to analysis using GC-MS. Comparative quantification of 7,11-hexadecadienal, oleic Acid and stigmasterol were carried out. It has been found that the soil containing 60% sewage sludge yielded maximum quantity of 7,11-hexadecadienal, oleic Acid and stigmasterol. Therefore, optimization of soil with different ratios of sewage sludge is carried out and 60% ratio of sewage sludge in soil is recommended for the promising growth of Momordicacharantia.