Agricultural Use of Urban Sewage Sludge from the Wastewater Station in the Municipality of Alexandria in Romania

Abstract

Considering the increase in the amount of sewage sludge as a result of the development of urbanization, and the pollution of the environment through the storage of this sludge, the objective of this paper is to analyze the effects of the action of different doses of urban sewage sludge as a fertilizer for agricultural soil. Starting from the legislative recommendations regarding the use of urban sewage sludge in agriculture, we analyzed the sludge resulting from the sewage treatment plant in the Municipality of Alexandria, Romania. This sewage treatment plant, with two technological lines of water and sludge treatment, produces urban sewage sludge without pathogenic bacteria. We highlighted that by applying sewage sludge doses of 15 t/ha and 25 t/ha to agricultural soils, on which we planted soybean and wheat crops. We obtained high yields, and the concentration of heavy metals in the roots, stems and grains of soybean and wheat crops did not exceed the maximum standard limits allowed. Having a high content of organic matter and nutrients important for plants such as nitrogen, ammonium, potassium and zinc, sewage sludge has improved the fertility, physical, chemical and biological properties of the soil, and is able to be used as a fertilizer for degraded soils.

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.…”

“…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] ; …”

Lead and copper removal from sterile dumps by phytoremediation with Robinia pseudoacacia

“…Generally, the dewatered sludge resulting from urban sewage treatment plants is composed of 20% fats, 50% carbohydrates (sugar, starch, and fiber), 30–40% organic matter, 3% total nitrogen, 1.5% total phosphorus, and 0.7% total potassium, has a C:N ratio of 10–20 and a neutral pH and it is often used as an organic fertilizer for acidic soils improving the soil physico-chemical properties, being an ecological alternative to chemical fertilizers 26 , 64 . The dewatered sludge resulting from the Someș sewage treatment plant did not record traces of heavy metals.…”

“…Therefore, the improvement of plant growth conditions by amendments and by treatments (fertilizers) to create larger nutrient concentration, larger water retention capacity, and an improved macrobiotic community in the root areas have been listed among complementary remediation strategies to phytoremediation 25 . Furthermore, mixing the sterile material with unpolluted soil, compost, or organic wastes like dewatered sludge resulting from sewage treatment plants to positively influence plant growth, achieve better plant nutrient statuses, and modify the physical–chemical properties of mine substrates have also been reported in studies of soil and tailing dams 24 – 26 .…”

Nutrient management: as a panacea to improve the caryopsis quality and yield potential of durum wheat (Triticum turgidum L.) under the changing climatic conditions

“…The use of sewage sludge fertilizers can have significant agronomic benefits, such as providing nutrients such as nitrogen, ammonium, potassium, and zinc and thus improving soil quality ( Marin and Rusănescu, 2023 ). When sewage sludge is applied to the soil, it can indeed improve soil organic matter (SOM) content, nutrient contents, soil porosity, bulk density, aggregate stability, and available water holding capacity ( Simões-Mota et al., 2022 ).…”