Effects of paper-mill industry treatment plant sewage sludge and Pseudomonas bacteria on soil biological characteristics and acidity reclamation

Abstract

This study aimed to evaluate the effects of two paper mill wastewater sludge (PMS) application rates—2% and 4% (w/w)— with and without Pseudomonas sp. inoculation, on soil pH, organic carbon (OC), microbial respiration (MBR), microbial biomass carbon (MBC), and cellulase activity in two acidic soils over a six-months incubation period. The soils had initial pH values of 4.62 (Soil-1) and 5.47 (Soil-2). PMS raised pH in both soils within the first month to 7.8 and 8.2 in Soil-1 and Soil-2, respectively, with greater increases at 4% and in Soil-2; Pseudomonas did not significantly affect pH. OC increased with PMS, more so when combined with bacteria, though it decreased over time. PMS markedly amplified MBR, especially in Soil-1, where the 4% PMS treatment yielded the highest response (0.6 mgCO₂ g_{dry soil} day⁻¹). MBC also rose, notably in Soil-2 at 2% PMS with bacteria inoculation (1.3 mgC g_{dry soil}⁻¹), indicating pH-dependent microbial responses. MBC trends mirrored those of MBR, initially increasing and then stabilizing or slowly declining. Both soils showed increased cellulase activity under PMS, more pronounced in Soil-1; bacteria sometimes modulated the trend differently between soils. The highest activity (380.46 μg GE g⁻¹ _{dry soil} day⁻¹) was recorded in the 4% PMS inoculated with bacteria. Overall, the combined use of PMS and Pseudomonas sp. represents a novel, low-cost strategy that simultaneously valorizes an industrial by-product and accelerates microbial-driven soil restoration — offering a sustainable alternative to conventional chemical amendments for managing degraded acidic soils.