Purpose The research was focused on evaluating phytotoxicity of sewage sludge from two selected wastewater treatment plants in Czech Republic. Methods Laboratory experiments were carried out with samples of sewage sludge, which were focused on the evaluation of their phytotoxicity by using the PhytotoxkitTM testing set. Specifically, the inhibitory/stimulating effect was established on the growth of roots from the seeds of white mustard (Sinapis alba L. ). The chosen proportions of sewage sludge were 10%, 30% and 50%. The test was conducted in three repetitions. Additionally, the research also included a comparison of the effect of compost addition to the sewage sludge and its potentially increased stimulating effect on the growth of roots from the seeds of white mustard (Sinapis alba L. ). Ratios of compost were 5%, 15%, 25% and 50%. The test was conducted in three repetitions. Results Stimulating effect on the growth of white mustard (Sinapis alba L. ) was demonstrated only in samples with the sludge proportion of 10%. The results also show that the addition of compost reduced phytotoxicity of sewage sludge in all three tested ratios (5%, 15%, 25% and 50%). Conclusion It was found out that the addition of compost resulted in the decreased phytotoxicity of all tested sewage sludge samples, and hence in their suppressed inhibitory effect.

Sewage sludge is widely used as a fertilizer and soil conditioner on agricultural lands. However because of high concentration of soluble salts in sewage sludge, it increases soil salinity. The objective of this study was to evaluate the residual and cumulative effects of sludge application on soil salinity. This study was conducted in Lavark experimental site with four rates (0, 25, 50 and 100 ton.ha-1) of sewage sludge. The plots received one, two, three or four years of sludge applications. Corn (Zea mays) and wheat (Triticum sativum) were planted in the first and second half of each year, respectively. Soil samples were collected at the end of wheat growing season at 20 cm increments to 100 cm depth from each plot. Soil samples were analyzed for EC, OC, Na, K, Mg, Ca, Cl, SO4 and HCO3. Sludge application significantly increased concentration of Na, Ca, K and Mg in the soil depths. Concentration of Cl, SO4 and HCO3 also significantly increased with sludge application. However, the effect of residual sludge application on soil salinity was minimal and because of leaching, soil EC did not reach the critical value that affect most plant growths.

In recent decades, disposal of dry sludge have been an important problem of sewage treatment plants due to environmental restrictions. The material is not usually permitted to be buried in soil or used as agricultural fertilizer because of high heavy metal contents. Some investigations performed on application of these materials in construction materials especially concrete mix designs. In this research, application of dry sludge produced in the Alborz (Qazvin) industrial/domestic sewage treatment plant in mass concrete at water to cement (w/c) ratios of 0.55 and 0.45 was investigated. The dry sludge was characterized for chemical composition (XRF analysis), crystalline phases (XRD analysis) and pozzolanic activity (Thermal gravimetery). Thereafter, it was used at 0, 5, 10, 20 and 30% of cement content in concretes. Effect of the dry sludge on compressive strength at different ages of curing 3, 7, 28 and 90 days was investigated. Besides, flexural strength, water absorption and porosity of concretes containing 20% dry sludge were measured after 28 and 90 days of curing. It was found that using dry sludge at 5, 10 and 20% caused decrease in compressive strength about 9, 14.5 and 29% in 28 days cured and 3.5, 8 and 20% in 90 days cured specimens in comparison to control specimens, respectively.

Production of vermicompost from sewage sludge is one of the suitable methods for convert of this waste to organic fertilizer. In this study, effects of decomposition stage of sludge and bulking materials on growth of earthworms were investigated. Experimental design was split factorial in three replications. The main factor was the stage of sewage decomposition (raw sewage, digested sludge in digester, dewatered sludge in lagoons, and final dried sludge in lagoons), and kind of bulking materials (woodchips, tree leaves, and wheat straw) and mixing proportion of bulking materials to swage sludge (0, 15, 30, and 45 %, V/V) were as subordinate factors. After 5 months incubation of pots in controlled moisture and temperature conditions, numbers of worms, cocoons, wet body weight of worms, and concentration of nutrients and heavy metals in produced vermicompost were measured. Population of worms, their body weight and cocoon production were highest in the pots contain final dry sludge. The  growth and reproduction of earthworms were greater when wood chips used as bulking material for vermicompost production. There was no significant difference between wheat straw and tree leaves in this respect. The suitable mixing proportion of bulking material and sewage sludge was 30 % (V/V). Therefore, mixing of wood chips with dry sewage with the proportion of 30 % (V/V) for vermicompost production and use of this technique to improve the stability of sewage sludge produced in sewage treatment plants are recommended.

To study the effects of sewage sludge on tomato seedling growth, a series of pot experiments, each pot containing 17 kg soil, were conducted in a randomized complete design with eight replications. Treatments used were: 5 levels of sewage sludge (5, 10, 20, 30 and 40 tons/ha) and two control treatments (T1, without sewage sludge and T2, sewage sludge + complete fertilizers). Analysis of variance for above ground fresh and dry weights showed that they were significantly higher than T2 (sludge + complete fertilizer) when 5 and 10 tons per hectare of sewage sludge were applied to the pot at %1 level of probability. Application of sewage sludge higher than 10 tons per hectare, due to its toxic effect, decreased fresh and dry weight of above ground plant parts drastically. For example, applying 30 tones sewage sludge decreased dry weight by 20 percent and fresh weight by 44 percent as compared with that of T2. Mean comparisons revealed that water content of tomato plants did not differ significantly in comparison with that of T2 when 10-20 tons of sewage were applied, but its difference was significant at 5 percent level of probability when 30 and 40 tons of sewage sludge were applied. Analysis of variance for dry, fresh and water content of fruit also showed that their differences with T2 were non- significant when 5 and 10 tons/ha sewage sludge were applied to the pots. However, applying sewage sludge beyond 10 tons per hectare reduced all these three attributes significantly. Applying 20, 30 and 40 t/ha of sewage sludge delayed growth and development and caused apparent necrosis in the leaf margins of young and mature plant within the first month, while the toxic effect of sludge on necrosis decreased at later growth stages. Higher availability of iron (Fe) at higher sludge application rates along with soluble cation and anion concentrations in soil solution, especially chlorine and probably other side effects caused by sludge application are the factors that may have toxic effects on plants.

Aims of the Study: The aim of this study was to determine the amount of lignin degradation and biodegradation of organic matter and change of biomass under compost and vermicomposting of sewage sludge.Materials & Methods: Sawdust was added to sewage sludge at 1: 3 weight bases to Carbon to Nitrogen ratio of 25: 1 for composting or vermicomposting. Lignin and volatile solids were determined at different periods, of 0, 10, 30, 40 and 60 days of composting or vermicomposting period to determine the biodegradation of lignocellulose to lignin. Results were expressed as mean of two replicates and the comparisons among means were made using the least significant difference test calculated (p<0.05).Results: After 60 days of experiment period, the initial lignin increased from 3.46% to 4.48% for compost and 3.46% to 5.27% for vermicompost. Biodegradation of lignocellulose was very slow in compost and vermicompost processes. Vermicomposting is a much faster process than compost to convert lignocellulose to lignin (p<0.05). Conclusions: The organic matter losses in sewage sludge composting and vermicomposting are due to the degradation of the lignin fractions. By increasing compost age, the amount of volatile solids will decrease.