Evaluating the effects of sewage sludge compost applications on the microbial activity, the nutrient and heavy metal content of a Chernozem soil in a field survey

Abstract

Sewage sludge contains organic matter and micro and macronutrients which are potentially useful for agricultural usage. However, it can be harmful when containing undesirable amounts of organic pollutants, heavy metals, or pathogens. Our study focused on examining the changes in the extractable nutrient, organic matter and heavy metal contents of a Chernozem soil and the alteration of the soil biological activity as a consequence of low-dose municipal sewage sludge compost applications (0.5 t/ha). Sampling campaigns were done in 2018 near Újkígyós (SE Hungary) during which composite soil samples (0–30 cm and 30–60 cm) and groundwater samples were collected for assessing changes in the nutrient and heavy metal concentrations as a result of compost amendments’ use. Additionally, upper soil (0–50 cm) and subsoil (50–80 cm) were sampled for assessing biological parameters, considered to be aerobic and anaerobic soil layers, respectively. Soil samples were analyzed for the basic pedological parameters (pH, organic matter, carbonates and texture), nutrients (K2O, P2O5, N-forms and organic matter) and heavy metal concentrations following standard extraction procedures. The microbial properties were characterized by colony-forming units (CFUs) and enzyme activity measurements. The results of the nutrient analyses show significantly increased soil-bound K2O, P2O5 and NO2− + NO3− contents linked to the sewage sludge treatments. However, neither the organic matter nor the heavy metal content varied significantly in the sludge-amended soil compared with a control site. The microbiological analyses revealed that the sewage sludge treatments tended to increase the aerobic CFUs, but not that of the anaerobic microbes. The average catalase enzyme activity in both the aerobic and anaerobic samples and the average dehydrogenase activity only in the aerobic layers showed a slight but not significant increase in the compost-amended soils. Overall, these results convincingly demonstrated that amending soils with low doses of municipal sewage sludge composts (lacking any industrial sources) can be a sustainable fertilizing practice taking advantage of their high N, P and K contents that are slowly converted to their bioavailable forms thus preventing their excessive leaching in the groundwater.

Physico-chemical characterization and possible uses of sludge processed from an urban sewage treatment plant

“…Regarding the heavy metals present in the sewage sludge that can be used in agriculture, all values registered for the analyzed samples (including their average value) are within the limits (towards the minimum limits) or even under the limits imposed by the worldwide normative acts in force [10] , [11] , [12] , [20] . Since all the requirements are achieved by the analyzed dried sludge, it can be further used with success in some branches of the agriculture domain, as follows: – Spreading on agricultural (excepting pastures, fruit tree plantations, and vegetable crops [12] ) or forestry land [32] : dehydrated sludge is very difficult to spread due to excessive moisture; by drying, the sludge becomes much easier to handle and can be spread with equipment used to spread manure; the composition of the analyzed sludge emphasizes there is no danger of contamination of the soil, plants, and humans; therefore, the dried sludge represents a safer type of fertilizer (compared to chemical ones); the condition is to quickly mix the dried sewage sludge with soil after application [33] ; – Completion of degraded areas with ruptures and damage [34] ; – Application on agricultural soil affected by runoffs, floodplains, or erosion: not recommended [35] ; – Making compost and flower soil [36] : dehydrated sludge in the preparation of flower soil is difficult to handle and requires a long period of drying under natural conditions, in order to be packed in bags. The smell of dehydrated sludge is often unpleasant; through the drying process, dehydrated sludge can acquire a pleasant odor by introducing flavored natural essences into the warm air; dried dehydrated sludge does not require drying periods after the preparation of the flower soil.…”

“…Making compost and flower soil [36] : dehydrated sludge in the preparation of flower soil is difficult to handle and requires a long period of drying under natural conditions, in order to be packed in bags. The smell of dehydrated sludge is often unpleasant; through the drying process, dehydrated sludge can acquire a pleasant odor by introducing flavored natural essences into the warm air; dried dehydrated sludge does not require drying periods after the preparation of the flower soil.…”

Plot-level field monitoring with Sentinel-2 and PlanetScope data for examination of sewage sludge disposal impact

“…Data collection based on remote sensing methods was performed for 14 homogenous quadrates having a size of 50x50 m2 on three agricultural plots producing different crops, in parallel with the soil sampling according to Farsang et al (2020). Certain quadrates represent areas treated with sewage sludge and the adjacent quadrates with very similar properties without treatment served as control areas for the study (Table 2).…”

Heavy Metal Remediation in Sludge Compost: Recent Progress

“…Sludge must pass through a series of treatments to ensure the safety of the products after composting [15]. Municipal sludge includes abundant heavy metals (e.g., zinc, copper, iron, and manganese) [16][17][18], organic matter, nitrogen, phosphorus, and nutrient elements [19], which are excellent soil amendments and manure after composting [20,21]. The many advantages of sludge composting include improved product safety, reduced biomass quality and volume, and a reduced late carbon nitrogen ratio [22].…”