Sewage sludge as a pedotechnomaterial for the recovery of soils compacted by heavy machinery on Eucalyptus commercial plantation

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.…”

Composted Sewage Sludge as a Substrate for Commercial Seedlings of Peltophorum dubium (Spreng.) Taub.

“…In contrast, commercial substrates (CSs) tend to be inert [25]. The high P and K amounts observed in CSs are due to the well-known presence of superphosphate added during its development process, mixed with carbonized rice husks, i.e., a potassium-rich material [32].…”

“…Furthermore, the growth of seedlings was reduced with the lower fertigation doses by the omission of P. According to Souza et al (2013) [51], P. dubium has growth limitations in terms of height and diameter in the absence of N, K, S, Ca, Mg, B, and Zn since the seedlings' demand for N and P is more significant in the initial seeding stages, which act in the initial growth of height and diameter [32].…”

“…As a matter of fact, seedling production represents an essential cost in soil restoration through reforestation programs [4]. One of the costs most affecting the overall commercial balance is represented by the use of commercial substrate [32]. Thus, by using by-products, this significant cost can be strongly reduced, making soil recovery and reforestation programs more feasible.…”