Using a second-order polynomial model to determine the optimum dregs/bark ratio for industrial-biosolid composting: the initial conditioning stage

Abstract

Increasing pulp industry production has generated additional solid waste (i.e. biological sludge, dregs, etc.) and therefore an increasing disposal problem. On the other hand, composting is emerging as an interesting alternative for the disposal of residues. The objective of this study was to evaluate the physical and chemical properties of sludge, dregs and bark and the effect on their initial conditioning stage prior to composting, using pine chips as bulking agent. After their characterization, these solid wastes were combined in different mixture proportions defined by a 32 experimental design based on the response surface methodology (RSM), in which 18 observations were required for the independent variables (dregs and bark) and the C: N ratio, moisture content and pH were the dependent variables. The characterization indicated that the dregs have alkaline properties with the presence of some essential plant nutrients, such as phosphorous (0.37%), potassium (0.76%), magnesium (1.4%) and calcium (27%). The combination of the macronutrients (phosphorous: 0.39%, potassium: 0.24%, calcium: 1.7%, magnesium: 0.44%) and micronutrients such as ferrous material (0.47%) and zinc (0.12%) found in the sludge suggest a promising alternative despite the potential problem due to the high pH of the dregs. The RSM design indicated a feasible region that satisfied the optimal dregs: bark ratio of 0.25 without exceeding the addition of 12.5% dregs, due to the alkaline properties of these inorganic wastes and the quadratic influence over the C:N ratio. The experimental results indicated that the composting process of dregs, bark and sludge is technically suitable, although the use of a rapidly available C source needs to be evaluated.

Microbial oxygen uptake in sludge as influenced by compost physical parameters

“…To maximize the statistical strength of experimental data while minimizing the number of experimental trials needed, a central composite factor design was used to test key levels of the physical parameters. Amongst the large number of papers dealing with composting, only a limited number in recent years are based on an experimental design that enhances the reliability of results (Liang et al, 2003;Gea et al, 2007;Zambrano et al, 2007;Bueno et al, 2008a;2008b).…”

An investigation on the nutrient and material effects of bark in komatsuna and tomato growing tests by using pots to determine the optimum mixed combination

“…Bark is generally perceived as a soil conditioning material or fertilizer, primarily because it is usually considered for its physical properties rather than its chemical properties. However, several studies researching the utility of bark as compost have been conducted in recent years [2,[12][13][14][15][16][17][18][19][20][21][22][23]. Many properties of bark material have yet to be elucidated.…”