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A potential bacterium Bacillus flexus RMWW II has been isolated from rice mill effluent, and examined for its decolorizing potential for lignin-mimicking dyes. The biodegradation of alkali lignin by the rod-shaped, Gram-positive, oxidase and catalase-positive Bacillus flexus RMWW II bacteria is due to its uptake of lignin as the sole carbon source. The lignin degradation was 100% at a lignin concentration of 50 mg L−1 but the degradation reduced to 20% at 400 mg L−1. The bacterial-mediated biodegradation of alkali lignin was suitably explained by the Edward kinetics model with a maximal specific biodegradation rate (qmax) of 0.056 h−1 and true specific biodegradation rate (q*) of 0.042 h−1. The non-toxic nature of the metabolites of alkali lignin after bacterial degradation was illustrated by phytotoxicity studies. This bacterium was utilized to treat complex rice mill wastewater, as lignin is one of the major components of the effluent. A considerable reduction of 84% of chemical oxygen demand (COD) was observed in a batch reactor in 70 h of operation. The bacterial treatment results for the actual rice mill effluent indicate that Bacillus flexus RMWW II could be a promising agent for microbial remediation of lignin-laden raw rice mill wastewater.

Fly ash (FA) from biomass combustion and biological sludge (S), both wastes from the pulp and paper industry, were granulated in different proportions (90% FA + 10% S, and 70% FA + 30% S w/w, dry weight basis, dw) and used to recover the functionality of soils affected by mining activities (Aljustrel, Iberian Pyrite Belt), with and without the application of municipal solid waste compost (MSWC). Application doses of both mixtures were 2.5, 5.0 and 10% (w/w, dw). These materials corrected soil acidity to circumneutral values and increased extractable P and K concentrations. A significant increase in soil organic matter (from 0.6 to 0.8–1.5% w/w, dw) and N content (from 0.04 to 0.09–0.12% w/w, dw) was also observed, but only when MSWC was applied. The soil was already heavily contaminated with Cu, Pb and Zn and the application of amendments did not increase their pseudo-total concentrations. The CaCl2 extractable fractions of both Cu and Zn decreased to very low values. The improvement in soil quality, compared to fertilizer only treatment, was further evidenced by the increase in some soil enzymatic activities (dehydrogenase, β-glucosidase and cellulase), with a better response for the granules with the higher proportion of biological sludge, as well as by the decrease in the soil-water extract toxicity towards different organisms (Daphnia magna, Thamnocephalus platyurus, and Pseudokirchneriella subcapitata). Agrostis tenuis germinated and grew during the first month only in the amended pots, but, after that, a considerable phytotoxic effect was evident. This was mainly attributed to salt stress or to some specific ionic toxicity. In conclusion, to establish a long-term plant cover in mining soils amended with biomass ash-based materials, the selection of plants with higher resistance to salinity and/or the stabilization of the amendments, to reduce their soluble salt content, is recommended.

Peat-based growing media are not ecologically sustainable and peat extraction threatens sensitive peatland ecosystem. In this study, olive-stone waste (OSW) and paper waste (PW) were used in different ratios—as growing media—for ornamental crop production, as peat (P) substitutes. Marigold (Calendula officinalis L.), petunia (Petunia x hybrita L.) and matthiola (Matthiola incana L.) plants were grown in (1) P (100%), (2) P:OSW (90%:10%), (3) P:OSW (70%:30%), and (4) P:OSW:PW (60%:20%:20%). The physicochemical properties of these substrates and the effects on plant growth were determined. The addition of 10–30% OSW into the substrate increased marigold height compared to plants grown in 100% peat. No differences in plant size, plant biomass (leaves and flowers), and dry matter content were found. Adding PW, in combination with OSW, maintained marigold height and total number of flowers produced to similar levels as in plants grown in 100% peat. In matthiola, adding 30% OSW into the substrate reduced plant size and fresh weight, but not plant height. No differences were observed when plants grew in lower OSW (i.e., 10%) content. Petunia’s height, its total number of flowers and flower earliness (flower opening) were increased in the presence of OSW compared to the plants grown in 100% peat. The addition of OSW did not affect petunia’s size and fresh weight among treatments. The addition of PW suppressed several plant growth-related parameters for both matthiola and petunia. The insertion of OSW did not change leaf chlorophyll content whereas the presence of PW decreased chlorophylls for marigold, petunia, and matthiola. Both OSW and PW altered the content of total phenolics and antioxidant capacity of 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) in leaves and flowers for marigold and petunia. Both 30% OSW and PW increased antioxidative enzyme metabolism due to the increased damage index and lipid peroxidation observed in plants. Leaf N and P content decreased in PW-based media, while matthiola displayed visual phytotoxicity symptoms when PW was added into the substrate. The present work indicates that up to 30% of OSW can replace peat for marigold and petunia growing and only up to 10% of OSW for matthiola, while the addition of PW on top of OSW is not recommended, so further research is needed.

The safe disposal of pulp and paper mill effluent is still a threat to the environment due to the presence of several unknown organic pollutants. The comparative physico-chemical analysis of pulp and paper mill effluent-contaminated sediment (PPECS) of site 1 and site 2 showed that the sediment had an alkaline nature and was loaded with several organic pollutants and heavy metals. SEM-EDX examination showed a porous structure with a heterogeneous distribution of particles, allowing the adsorption of metal and other complex organic ions. FTIR analysis depicted the presence of a variety of functional groups, i.e., alkyl halides, phenolics, and lignin, in the contaminated sediment. GC-MS analysis showed the major presence of organic pollutants, i.e., 2-methyl-4-keto-2-pentan-2-ol and 3,7-dioxa-2,8-disilanonane,2,2,8,8-tetramethyl-5-[(trimethylsilyl)oxy], in the site 1 sediment contaminated with pulp and paper mill waste, while 2-methyl-4-keto-2-trimethylsiloxypentane, 4-ethyl-2-methoxyphenol, ethyl-2-octynoate, cis-9-hexadecenoic acid, and octadecenoic acid were detected in the site 2 sediment contaminated with pulp and paper mill waste. The genotoxicity of PPECS determined by examining Allium cepa root cell division showed chromosomal aberration. In this study, several compounds that have not been reported before were identified.

Compost has been proposed as a means of simultaneously diverting organic materials from landfills while producing a valuable product that improves tilth, organic matter content and nutrient supply of agricultural soils. Composts manufactured from different source materials may have markedly different properties however, even if they meet all regulatory requirements. We compared the capacity of composts made from three different combinations of organic wastes (horse manure and bedding, mink farm wastes, municipal solid waste (MSW) and sewage sludge) along with clarifier solids from a chemo-thermomechanical pulp mill, to enhance the growth of tomato (Lycopersicon esculentum L.) seedlings grown in nutrient-poor organic potting soil. Germination and seedling emergence of tomatoes, cress (Lapidium sativum L.) or radish (Raphanus sativus L.) were tested to assess phytotoxicity of the four amendments. Mink farm compost and horse manure compost stimulated root and shoot growth of tomato seedlings but MSW compost and pulp mill solids were strongly inhibitory. MSW compost and unamended potting soil also inhibited seedling emergence and pulp mill solids produced stunting and deformities in radish and cress seedlings. Both toxic constituents and nutrient imbalances may be responsible for the growth-inhibiting effects of these amendments. Application of pulp mill solids to agricultural soil without composting may lead to deleterious effects on vegetable crops.