Effect of sewage sludge amendment on soil microbial activity and nutrient mineralization

An incubation experiment was performed to study the effect of sewage sludge on microbial respiration and nutrient mineralization in a sandy soil as an indication of its effects on soil biological properties and nutrient transformation. Sewage sludge was amended with a sandy soil at 0, 25, 50, 150 and 350 g kg⁻¹ fresh weight. An increase in the sludge amendment rate caused an increase in both pH and electrical conductivity (EC). However, pH decreased while EC increased and then decreased along the incubation time. Nevertheless salinity and heavy metal contents of the soil sludge mixture were all within the safety guidelines. Soluble NH₄⁺, NO₃²⁻ and PO₃²⁻ increased after amending the soil with sewage sludge, but increasing the application rate to 350 g kg⁻¹ of sludge decreased the N and P mineralization efficiency and created an adverse effect on nitrification. The daily CO₂ evolution pattern was the same in all treatments that CO₂ evolution increased initially and then decreased till the end of the incubation period. All the treatments had peak CO₂ evolution at day 7, except for the soil amended with 350 g kg⁻¹ of sludge which had peak CO₂ evolution at day 2. Similarly, the percentage of C-mineralization decreased with an increase in sludge amendment rate. The present experiment indicated that an application rate of 50–150 g kg⁻¹ sludge for sandy soil would have the optimal beneficial effect on the soil in terms of microbial activity and nutrient transformation.     

Discharge of swine wastes risks water quality and food safety: Antibiotics and antibiotic resistance genes from swine sources to the receiving environments

Swine feedlots are widely considered as a potential hotspot for promoting the dissemination of antibiotic resistance genes (ARGs) in the environment. ARGs could enter the environment via discharge of animal wastes, thus resulting in contamination of soil, water, and food. We investigated the dissemination and diversification of 22 ARGs conferring resistance to sulfonamides, tetracyclines, chloramphenicols, and macrolides as well as the occurrence of 18 corresponding antibiotics from three swine feedlots to the receiving water, soil environments and vegetables. Most ARGs and antibiotics survived the on-farm waste treatment processes in the three swine farms. Elevated diversity of ARGs was observed in the receiving environments including river water and vegetable field soils when compared with respective controls. The variation of ARGs along the vertical soil profiles of vegetable fields indicated enrichment and migration of ARGs. Detection of various ARGs and antibiotic residues in vegetables fertilized by swine wastes could be of great concern to the general public. This research demonstrated the contribution of swine wastes to the occurrence and development of antibiotic resistance determinants in the receiving environments and potential risks to food safety and human health.     

Does human activity impact the natural antibiotic resistance background? Abundance of antibiotic resistance genes in 21 Swiss lakes

Antibiotic resistance genes (ARGs) are emerging environmental contaminants, known to be continuously discharged into the aquatic environment via human and animal waste. Freshwater aquatic environments represent potential reservoirs for ARG and potentially allow sewage-derived ARG to persist and spread in the environment. This may create increased opportunities for an eventual contact with, and gene transfer to, human and animal pathogens via the food chain or drinking water. However, assessment of this risk requires a better understanding of the level and variability of the natural resistance background and the extent of the human impact. We have analyzed water samples from 21 Swiss lakes, taken at sampling points that were not under the direct influence of local contamination sources and analyzed the relative abundance of ARG using quantitative real-time PCR. Copy numbers of genes mediating resistance to three different broad-spectrum antibiotic classes (sulfonamides: sul1, sul2, tetracyclines: tet(B), tet(M), tet(W) and fluoroquinolones: qnrA) were normalized to copy numbers of bacterial 16S rRNA genes. We used multiple linear regression to assess if ARG abundance is related to human activities in the catchment, microbial community composition and the eutrophication status of the lakes. Sul genes were detected in all sampled lakes, whereas only four lakes contained quantifiable numbers of tet genes, and qnrA remained below detection in all lakes. Our data indicate higher abundance of sul1 in lakes with increasing number and capacity of wastewater treatment plants (WWTPs) in the catchment. sul2 abundance was rather related to long water residence times and eutrophication status. Our study demonstrates the potential of freshwater lakes to preserve antibiotic resistance genes, and provides a reference for ARG abundance from lake systems with low human impact as a baseline for assessing ARG contamination in lake water.     

Occurrence and removal of antibiotic resistance genes in municipal wastewater and rural domestic sewage treatment systems in eastern China

Antibiotic resistance genes (ARGs) are emerging environmental contaminants and pose a threat to public health. In this study, four tetracycline resistance genes (tetM, tetO, tetQ and tetW) and two sulfonamide resistance genes (sulI and sulII) were evaluated in 4 municipal wastewater and 8 rural domestic sewage treatment systems with different wastewater handling abilities and treatment processes using quantitative polymerase chain reaction (qPCR). In the influents, the relative abundance of different ARGs showed significant variations among the sampling sites. In addition, significant correlations (tetQ: R² = 0.712, P < 0.05; tetO: R² = 0.394, P < 0.05) between the gene copy numbers and wastewater-receiving capacity were observed. Statistical analysis revealed a positive correlation (R² = 0.756, P < 0.05) between the gene copy numbers of sulI and intI1, whereas the gene numbers of tetM and sulI were strongly correlated with 16S rDNA. Significant reductions (1–3 orders of magnitude) in ARGs were observed in municipal wastewater treatment systems, but a smaller reduction was found in the rural domestic sewage treatment systems. These results provide insights into the occurrence and removal of ARGs in wastewater treatment systems in both rural and urban areas in eastern China.     

A spatial multicriteria decision making tool to define the best agricultural areas for sewage sludge amendment

Sewage sludge amendment on agricultural soils has recently become a practice of heightened interest, as a consequence of sewage sludge production increase. This practice has benefits to soil and crops, however it may also lead to environmental contamination, depending on the characteristics of the fields. In order to define the suitability of the different agricultural fields to receive sewage sludge, a spatial tool is proposed. This tool, elaborated in GIS platform, aggregates different criteria regarding human exposure and environmental contamination.The spatial tool was applied to a case study in the region of Catalonia (NE of Spain). Within the case study, each step of the tool development is detailed. The results show that the studied region has different suitability degrees, being the appropriate areas sufficient for receiving the total amount of sewage sludge produced. The sensitivity analysis showed that “groundwater contamination”, “distance to urban areas”, “metals concentration in soil” and “crop type” are the most important criteria of the evaluation.The developed tool successfully tackled the problem, providing a comprehensive procedure to evaluate agricultural land suitability to receive sewage sludge as an organic fertilizer. Also, the tool implementation gives insights to decision makers, guiding them to more confident decisions, based on an extensive group of criteria.     

Identification of metal toxicity in sewage sludge leachate

Sewage sludge is a source of organic matter and nutrients with the potential for being used as a fertilizer. However, metals in sewage sludge might accumulate in soil after repeated sludge applications, and metal concentrations might reach concentrations that are toxic to microorganisms, soil organisms and/or plants. This toxicity might change with time due to kinetic factors or abiotic factors such as freezing, drying or rainfall. The objective of this study was to determine toxicity of sewage sludge leachate from a lysimeter with 50 cm of sludge applied. Attempts were also made to identify the cause of toxicity of the sludge leachate by toxicity identification and evaluation (TIE) techniques. Sludge leachate was collected monthly during 1 experimental year (August 2001 to August 2002). Metal concentrations were analysed, and the toxicity was determined with Daphnia magna (48-h immobility). The effect of EDTA or sodium thiosulphate addition, filtration through a CM-resin or a Millex-resin on toxicity was also tested. The results showed that toxicity of the sludge leachate apparently varied during the year, and that filtration through the CM-resin reduced most of the toxicity followed by the addition of EDTA. None of the other treatments reduced the toxicity of the sludge leachate. This indicated that one or more metals were responsible for the observed toxicity. Further calculations of toxic units (TU) suggested that Zn contributed most to the toxicity. Results also indicated that Ca concentrations in the sludge leachate reduced the toxicity of Zn.     

Comparative Analysis of Microbial Communities of Contrasting Soil Types in Different Plant Communities

Microbiomes were analyzed in samples of the major soil types of Russia and Western Kazakhstan region from different plant communities (fallow, forest, agrophytocenosis). The representatives of 42 bacterial and 2 archaeal phyla were identified in the samples, among which the dominant positions were occupied by representatives of ten phyla: nine bacterial (Actinobacteria (33.5%), Proteobacteria (28.4%), Acidobacteria (8.3%), Verrucomicrobia (7.7%), Bacteroidetes (4.2%), Chloroflexi (3.0%), Gemmatimonadetes (2.3%), Firmicutes (2.1%), Planctomycetes (2.0%)) and one archaeal Crenarchaeota (2.6%). Data analysis by the methods of multivariate statistics suggests that the taxonomic structure of microbiota is formed under the action of two main factors: the strongest factor is soil acidity, which determines the dynamics of the microbiome at the level of major taxa such as phylum, and the weaker factor is the type of vegetation, which determines the community structure at lower taxonomic level (order, family, genus). Detailed analysis of the samples of podzolic soil in Leningrad Region made it possible to identify bacterial taxa specifically associated both with the type of biome (fallow, forest, agrophytocenosis) and with the specific plant community (specific composition of plant synusia).     

Bioremediation of oil sludge-contaminated soil

Bioremediation has become an important method for the restoration of oil-polluted environments by the use of indigenous or selected microbial flora. Several factors such as aeration, use of inorganic nutrients or fertilizers and the type of microbial species play a major role in the remediation of oil-contaminated sites. Experiments were undertaken for bioremediation of oil sludge-contaminated soil in the presence of a bacterial consortium, inorganic nutrients, compost and a bulking agent (wheat bran). Experiments were conducted in glass troughs for the 90-day period. Bulked soil showed more rapid degradation of oil compared to all other amendments. During the experimental period, wheat bran-amended soil showed 76% hydrocarbon removal compared to 66% in the case of inorganic nutrients-amended soil. A corresponding increase in the number of bacterial populations was also noticed. Addition of the bacterial consortium in different amendments significantly enhanced the removal of oil from the petroleum sludge from different treatment units.     

Assessment of polychlorinated dibenzo-p-dioxins and dibenzofurans in sludges according to the European environmental policy

The amount of sewage sludge generated in Europe is expected to surpass the 10 million tons/year in 2006 as a result of the waste water treatment process according to the Water Policy in European Union. Sewage sludge is what is left behind after water is cleaned in waste treatment plants and is characterized for this high content in nitrogen and phosphorous that could be of great importance in agriculture as fertilizer or soil conditioner. On the other hand, pollutants like metals and organic contaminants are usually removed from water and are accumulated in the sewage sludge, reaching the food chain if their concentrations are not below the safe limits established by the European legislation. The latter issue is of great concern nowadays and in this sense, different works alert against the use of the sewage sludge in agriculture arguing that serious illnesses, even resulting in death as well as adverse environmental impacts are associated to the application of sewage sludge. This work is a continuation of a former comprehensive survey on of priority organic pollutant in sludges for agricultural purposes carried out by our group in Catalonia and this time is focused on the polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F), one of the most toxic group of organic compounds listed in the Work Document on Sludge which is the reference tool in this field in Europe and is also included in the Stockholm Convention. Eighty eight samples were collected from the end of 2003 to April 2006 and the concentrations detected were lower than the 100 ng/kg I-TEQ limit recommended by the European legislation (EC, 2000). Thus, sewage sludges generated in Catalonia do not represent a threat to human health if they are used as fertilizers in agriculture.     

The stabilization of sewage sludge by pulverized fuel ash and related materials

In Hong Kong, with the implementation of the Strategic Sewage Disposal Strategy (SSDS), there will be a substantial increase in the generation of sewage sludge. An alternative method using pulverized fuel ash (PFA) generated from a local coal fire power station and lime to stabilize the sludge for potential beneficial uses is studied. The effects of the stabilizing agents on the leaching of heavy metals and pasturing of coliform are studied. The results show that PFA together with a small percentage of lime addition has the potential to reduce heavy metal leaching and reduce the total coliform content of the stabilized sewage sludge.     

Toxicity of copper in sewage sludge

Sewage sludge is a source of organic matter and nutrients, but a major obstacle for its recycling is that the municipal wastewater sludge has low but significant levels of contaminants. This investigation, on the acute toxicity of copper in sewage sludge, was conducted with three organisms, Daphnia magna, Lemna minor and Raphanus sativus (seeds). The toxicity of the leakage water from sewage sludge spiked with CuSO(4) was studied for 64 days. The toxicity increased during the first 8-16 days and then started to decrease. The first increase in toxicity was due to ammonia, but after 32 days, a dose-related effect of copper was found. After 64 days, L. minor had an EC50 of 3800 mg Cu/kg dw for 7 days growth inhibition, a LOEC of 3200 mg Cu/kg dw and a NOEC of 1600 mg Cu/kg dw. D. magna had an EC50 of 18100 mg Cu/kg dw (24-h immobility) and a NOEC of 12800 mg Cu/kg dw. Root elongation of R. sativus was reduced at 25600 mg Cu/kg dw. Both for Daphnia and Lemna, the pH of the leakage water had an effect of the toxicity. This means that chemical speciation and bioavailability is very important for the hazard assessment of copper in sludge and soil.     

Effect of phytoremediation in technogenic landscapes of mining areas on the functioning of actinomycete communities

It has been shown that conditions formed in technozems of tailing dumps covered with a layer of chernozem are optimal for the development of soil microflora, including actinomycetes, as follows from their high abundance. The use of Leymus sabulosus (Bieb.) Tzvel in biological remediation of technozems formed in tailing dumps ensures an increase not only in the abundance of microorganisms in edaphotopes but also in their ecological diversity, compared to technozems planted with Rhus hirta (L.) Sudw, as confirmed by 1.2- and 1.9-fold increase in the Margalef and Berger–Parker diversity indices. Therefore, applying a layer of chernozem on technozems of tailing dumps provides for more efficient remediation of technogenic soils.     

Modeling of Cs migration in soils using an 80-year soil archive: role of fertilizers and agricultural amendments

An 80-year soil archive, the 42-plot experimental design at the INRA in Versailles (France), is used here to study long-term contamination by ¹³⁷Cs atmospheric deposition and the fate of this radioisotope when associated with various agricultural practices: fallow land, KCl, NH₄(NO₃), superphosphate fertilizers, horse manure and lime amendments. The pertinence of a simple box model, where radiocaesium is supposed to move downward by convectional mechanisms, is checked using samples from control plots which had been neither amended, nor cultivated since 1928. This simple model presents the advantage of depending on only two parameters: α, a proportional factor allowing the historical atmospheric ¹³⁷Cs fluxes to be reconstructed locally, and k, an annual loss coefficient from the plow horizon. Another pseudo-unknown is however necessary to run the model: the shape of historical ¹³⁷Cs deposition, but this function can be easily computed by merging several curves previously established by other surveys. A loss of ∼1.5% per year from the plow horizon, combined with appropriate fluxes, provides good concordance between simulated and measured values. In the 0–25 cm horizon, the residence half time is found to be ∼18 yr (including both migration and radioactive decay). Migration rate constants are also calculated for some plots receiving continuous long-term agricultural treatments. Comparison with the control plots reveals significant influence of amendments on ¹³⁷Cs mobility in these soils developed from a unique genoform.     

Scanning electron microscopic studies and growth response of the plants of Helianthus annuus L. grown on tannery sludge amended soil

The plants of Helianthus annuus L. var. modern were grown in the soil amended with different amounts of tannery sludge (10%, 25%, 35%, 50%, 75% and 100%), collected from Wastewater Treatment Plant Jajmau, Kanpur (Uttar Pradesh, India) under field conditions. The effect of tannery sludge amendments was studied on the growth performance of the plant, i.e. root length, shoot length, leaf area and number of leaves after 30, 60 and 90 days of exposures. The root length of the plant increased up to 35% tannery sludge followed by significant (p<0.01) decrease at higher amendments, whereas the shoot length of the plant increased with increase in sludge amendment ratio at all the exposure periods, compared to their respective controls. The number of leaves and leaf area in the plants of H. annuus increased at all the amendments of tannery sludge at initial exposure periods (30 and 60 days); however, it decreased at higher sludge amendments at highest exposure period (90 days) as compared to their respective controls. The analysis of scanning electron micrographs of the leaf surface of H. annuus grown on 50% and 100% tannery sludge after 90 days showed an increase in the frequency of stomata and trichomes, closure of stomata and degeneration of certain cells in the sludge grown plants.     

Development of a rapid method for direct detection of tet(M) genes in soil from Danish farmland

A method for direct detection of antibiotic resistance genes in soil samples has been developed. The tetracycline resistance gene, tet(M), was used as a model. The method was validated on Danish farmland soil that had repeatedly been treated with pig manure slurry containing resistant bacteria. The tet(M) gene was directly detected in 10-80% of the samples from the various farmland soils and could be detected in all samples tested after selective enrichment. To validate the obtained results, the method was applied to garden soil samples where lower prevalence of resistance was found. RESULT: A detection limit of 10(2)-10(3) copies of the tet(M) gene per gram of soil (in a Bacillus cereus group bacterium) was achieved. tet(M) gene was detected in soil samples with the highest prevalence on farmland treated with pig manure slurry.     

Development of extraction method of pharmaceuticals and their occurrences found in Japanese wastewater treatment plants

In this study, occurrence of 66 PPCPs (pharmaceuticals and personal care products) in liquid and solid phases of sewage sludge was elucidated. The extraction methods for the PPCPs from sludge were newly developed employing Pressurized Liquid Extraction (PLE) and Ultrasonic Solvent Extraction (USE). As an appropriate method, PLE using water (pH2), PLE using methanol (pH4), and USE using mixture of methanol and water (1/9,v/v, pH11) was found most effective because total recovery of most of the PPCPs indicated 40 to 130%. The developed extraction method with previously developed method for liquid phase analysis was applied to field survey at wastewater treatment plants (WWTPs) in Japan. 56 compounds were detected from the primary sludge and 61 compounds were detected from the excess sludge. The concentration was ranged between several ng/g and several μg/g. Solid-water distribution coefficient (Log K_d) ranged between 0.9 L/kg (Caffeine) and 3.7 L/kg (Levofloxacin) for primary sludge and between 1.4 L/kg (Sulpirid) and 4.3 L/kg (Mefenamic acid) for excess sludge.     

Distributions of zinc, copper, cadmium and lead in a tropical ultisol after long-term disposal of sewage sludge

Heavy metals present in soils constitute serious environmental hazards from the point of view of polluting the soils and adjoining streams and rivers. The distribution of heavy metals in a sandy Ultisol (Arenic Kandiustult) in south eastern Nigeria subjected to 40 years disposal of sewage wastes (sludge and effluents) was studied using two profile pits (S/NSK/1 and S/NSK/2) sited in the sewage disposal area and one profile pit (NS/NSK) sited in the non-sewage disposal area. Soil samples were collected in duplicate from these soil horizons and analyzed for their heavy metal contents. The mean concentrations of Zn, Cu, Cd and Pb in the top- and sub-soil horizons of sewage soil were 79.3, 32, 0.29 and 1.15 mg/kg, respectively. These levels were high enough to constitute health and phytotoxic risks. All the metal levels were much higher in the AB horizon in the sewage than in the non-sewage soil profile, but Pb and Cu contents were also high down to the Bt1 horizon, indicating their apparent relatively high mobility in this soil. There was a significant correlation between organic matter (OM) and Zn (r=0.818**), and between OM and Cd (0.864**) in the sewage soil. The high OM status of the sewage sludge, together with its corresponding low pH, might have favoured metal-OM complexation that could reduce heavy metal mobility and phytotoxicity in this soil.     

Airborne dissemination of bacteria from sewage treatment plants

During the last 5 yr, the air of sewage treatment plants was examined bacteriologically under different climatic conditions. Methods of examination were sedimentation on nutrient agar, membrane filtration and the use of an impinger. At each sampling site wind velocity and humidity of air were measured. In addition to colony counts, the presence of fecal indicators (E. coli, Clostridia), Salmonella, non-agglutinable cholera vibrios and Pseudomonas aeruginosa was determined. The results were as follows: The formation of mist above the sewage in aeration tanks was preferably observed during the winter season. Correspondingly, the bacteriological results were less favourable in winter-time; trickling filters are also capable of spreading bacteria into ambient air; E. coli could be found up to a distance of 300 m downwind from the aeration tanks, Salmonella up to a distance of 10 m; higher wind velocity resulted in a higher number of positive findings, sunshine diminished it, covering of the aeration tanks clearly resulted in a lower number of positive findings, parallel examinations performed at other sampling sites far from sewage treatment plants, such as underground stations, shops, or sports facilities revealed that the bacterial level at such sites was much lower than in the air of sewage treatment plants. Quantitative studies (Salmonella was taken as an example) revealed that the dissemination by air was low in relation to the Salmonella content of the sewage itself, so that the infectious dose was hardly attained by direct ingestion. Nevertheless, hygienic measures, such as hand washing, use of protecting clothes and avoidance of contact with foods in the open air should be performed in sewage treatment plants so that the infectious dose also cannot be indirectly reached. Beyond this, the possibility cannot be ruled out that conditions are quite different for other pathogens having much lower infectious doses.     

Abundance and community structure of bats (Chiroptera: Vespertilionidae) hibernating in artificial caves of Samarskaya Luka

The structure of hibernating bat communities has been studied in eight artificial caves of Samarskaya Luka differing in size and layout. Three types of the relative abundance distribution (RAD) of species in these communities have been revealed. Conditions for hibernation are most favorable in large caves with a stable microclimate, where the abundance of bats is high, the Shannon index has the peak values, and variation in the index of species evenness is the lowest. In such caves, RAD fits the broken-stick and log-series models. Variation in diversity indices reaches the highest level in shallow adits with a changeable microclimate, where RAD fits the geometric series model. The abundance, diversity, and structure of communities depend mainly on cave size and the presence of absence of drafts and, to a lesser extent, on ambient temperature, availability of microshelters, and the type of landscape surrounding the cave. Anthropogenic factors have a weak effect only on the abundance of individual species (M. nattereri, M. daubentonii, M. dasycneme, and E. nilssonii) but not on the overall diversity of bat communities.     

Effects of earthworm activity on fertility and heavy metal bioavailability in sewage sludge

The potential for using earthworms (Eisenia fetida) to improve fertility and reduce copper and cadmium availability in sewage sludge was tested by laboratory incubation experiments. Results comparing sewage sludge with and without earthworm treatment showed that earthworm activity decreased the contents of organic matter, total nitrogen, but increased the contents of available nitrogen and phosphorus and had no significant effect on the contents of total phosphorus, total potassium and available potassium. After incubation of the sewage sludge with earthworms for 60 days, the contents of Cu and Cd in the earthworms increased with the increase of additional Cu up to 250 mg kg(-1) and Cd up to 10 mg kg(-1). Bioconcentration factors (BCF) were higher than 1 only for Cd when the addition rate was lower than 5 mg kg(-1), which indicates that the earthworms can only accumulate Cd when the concentration of Cd is low in sewage sludge. Bioavailability of Cd and Cu was evaluated by applying sewage sludge with and without earthworm treatment to soil and then growing cabbage plants. The results showed that earthworm treatment increased the biomass of cabbage and decreased the bioaccumulation of Cd and Cu in the cabbage plants.