Pulp Mill Biosolids Research Articles

Pulp mill biosolids mitigate soil greenhouse gas emissions from applied urea and improve soil fertility in a hybrid poplar plantation

Pulp mill biosolids (hereafter 'biosolids') could be used as an organic amendment to improve soil fertility and promote crop growth; however, it is unclear how the application of biosolids affects soil greenhouse gas emissions and the mechanisms underlying these effects. Here, we conducted a 2-year field experiment on a 6-year-old hybrid poplar plantation in northern Alberta, Canada, to compare the effects of biosolids, conventional mineral fertilizer (urea), and urea + biosolids on soil CO2, CH4 N2O emissions, as well as soil chemical and microbial properties. We found that the addition of biosolids increased soil CO2 and N2O emissions by 21 and 17%, respectively, while urea addition increased their emissions by 30 and 83%, respectively. However, the addition of urea did not affect soil CO2 emissions when biosolids were also applied. The addition of biosolids and biosolids + urea increased soil dissolved organic carbon (DOC) and microbial biomass C (MBC), while urea addition and biosolids + urea addition increased soil inorganic N, available P and denitrifying enzyme activity (DEA). Furthermore, the CO2 and N2O emissions were positively, while the CH4 emissions were negatively associated with soil DOC, inorganic N, available phosphorus, MBC, microbial biomass N, and DEA. In addition, soil CO2, CH4 and N2O emissions were also strongly associated with soil microbial community composition. We conclude that the application of the combination of biosolids and chemical N fertilizer (urea) could be a beneficial approach for both the disposal and use of pulp mill wastes, by reducing greenhouse gas emissions and improving soil fertility.

Use of pulp mill biosolids to stimulate forest plant growth on an industrial footprint with marginal soil

Land application of biosolids may be an effective strategy to improve soil quality and better support the establishment of native vegetative cover on an industrial footprint with marginal soil. Biosolids can influence the C sequestration potential of impacted soils at the onset of reclamation activities by facilitating soil development processes and enhancing primary productivity, thereby leading to an increase in soil organic carbon (SOC) accumulation.The objective of this study was to examine the ameliorative effects of biosolids originating from a regional pulp and paper company on soil and vegetation development at a reclaimed airstrip in NW Alberta with limited topsoil replacement. Three biosolids application treatments (0 [control], 6.2, and 15.5 T ha−1) were established and vegetation was monitored by measuring percent cover and woody species density, height, biomass, and total nitrogen in aboveground biomass. The effects of biosolids on soil bulk density, various chemical properties including total organic carbon (TOC), nitrate (NO3), phosphorous (P), soil organic matter (SOM) and vegetation growth and establishment were evaluated over five growing seasons after initial application.One-time application of biosolids at 15.5 T ha−1 decreased soil bulk density, significantly increased other soil chemical properties (e.g., TOC, NO3, SOM), and improved native species vegetation establishment and growth significantly over the five growing seasons. These findings have implications for improving the efficiency and reducing the cost of reclamation in industrial footprints with marginal soil properties (high bulk density, low total organic carbon and nitrogen) using a by-product from forestry companies to ameliorate the soils

Seasonal Microbial Population Shifts in a Bioremediation System Treating Metal and Sulfate-Rich Seepage

Biochemical reactors (BCRs) using complex organics for bioremediation of mine-influenced water must operate successfully year round. In cold climates, where many mines in Canada are located, survival of the important microorganisms through the winter months is a concern. In this work, broad phylogenetic surveys, using metagenomics, of the microbial populations in pulp mill biosolids used to remediate metal leachate containing As, Zn, Cd and sulfate were performed to see if the types of microorganisms present changed over the seasons of one year (August 2008 to July 2009). Despite temperature variations between 0 and 17 °C the overall structure of the microbial population was fairly consistent. A cyclical pattern in relative abundance was detected in certain taxa. These included fermenter-related groups, which were out of phase with other taxa such as Desulfobulbus that represented potential consumers of fermentation byproducts. Sulfate-reducers in the BCR biosolids were closely related to psychrotolerant species. Temperature was not a factor that shaped the microbial population structure within the BCR biosolids. Kinetics of organic matter degradation by these microbes and the rate of supply of organic carbon to sulfate-reducers would likely affect the metal removal rates at different temperatures.

Empirical modeling of the effects of emerging pretreatment methods on anaerobic digestion of pulp mill biosolids

Effects of sludge type, microwave temperature, sonication time, and anaerobic digester temperature were investigated on solubilization and methane production from pulp mill secondary and primary sludges by multi-level factorial designs. Analysis of variance showed that all main effects (microwave temperature, sludge type and digestion temperature) and two-way interactions have significant (P-value<0.05) effects on cumulative methane production relative to control (not pretreated) digesters (CMPr) at elevated microwave temperatures (150–175°C). On the other hand, at lower microwave temperatures (50, 75, and 100°C), pretreatments did not significantly improve the CMPr. During the sonication, sonication time and digestion temperature significantly affected the CMPr with a P-value<0.05. The variance analysis also determined that, for both pretreatment methods, the most important factor affecting the sludge solubilization, indicated by the relative to control soluble to total chemical oxygen demand ratio (SCOD/TCODr), was the sludge type. To select a pretreatment/digestion that maximizes both the rate as well as the extent of anaerobic biodegradation, the technique for order preference by similarity to ideal solution (TOPSIS) was applied and it was concluded that mesophilic anaerobic digestion of pulp mill secondary sludge irradiated at 125°C can result in an optimal pretreatment scenario with SCOD/TCODr and CMPr of 6.1, and 1.7, respectively.

Empirical Modeling for Effects of Emerging Pretreatment Methods on Anaerobic Digestion of Pulp Mill Biosolids

Empirical Modeling for Effects of Emerging Pretreatment Methods on Anaerobic Digestion of Pulp Mill Biosolids

Correlation of bacterial communities supported by different organic materials with sulfate reduction in metal-rich landfill leachate

Several different organic materials, typical of those used in passive treatment systems for mine influenced water, were tested for their ability to support sulfate-reducing bacteria and sulfate reduction in an anaerobic biological reactor (ABR). The quantity of sulfate-reducing bacteria (SRB) in each organic material, as determined using quantitative polymerase chain reaction (q-PCR) of the dissimilatory sulfite reductase (dsr) gene, correlated with the initial C/N ratio of each material. Potential sulfate reduction rates measured in the laboratory ranked silage > compost = molasses/hay > cattails > pulp mill biosolids and correlated with the q-PCR estimates of SRB in the submerged materials. A comparison of bacterial communities using 16S rRNA gene clone library sequencing revealed similar distribution of clones among the phyla Bacteroidetes, Firmicutes and Proteobacteria for silage, compost and molasses/hay after 174 days of exposure in the seepage water. Silage, the most successful material tested, contained more δ-Proteobacteria-related sequences than the other materials and Spirochaetes-related clones were more abundant in silage than in compost or molasses/hay. According to sequenced dsr clones, the SRB community in silage differed from that for compost and molasses/hay, with fewer Desulfovibrio- and more Desulfomicrobium-related sequences in the silage. Pulp mill biosolids used in the ABR since 2004 contained an overall bacterial community that was more diverse than those for the freshly submerged organics, but only Desulfovibrio desulfuricans-related sequences were found in the dsr library.

Assessing the impact of land-applied biosolids from a thermomechanical (TMP) pulp mill to a suite of terrestrial and aquatic bioassay organisms under laboratory conditions

The potential impact on a variety of bioassay organisms when pulp-mill biosolids from a thermomechanical pulp mill (western Canada) were applied to a reference soil has been investigated in a laboratory setup. The current research assessed acute, chronic, and reproductive impacts using a battery of terrestrial and aquatic organisms. Terrestrial organisms were exposed to soil amended with different concentrations of biosolids, while aquatic organisms were used to assess the impact of biosolids’ runoff into receiving waters. The former bioassays showed that an application rate of 20 tonnes hectare −1 (t ha −1) “bone-dry” biosolids applied to reference soil produced no observable adverse impact on the terrestrial organisms. In the latter assays, undiluted (100%) and 50% diluted biosolids’ runoff into receiving water had a detrimental impact on the aquatic organisms. However, concentrations not exceeding 25% (environmentally relevant concentrations) had neither an acute nor chronic impact compared to reference populations. The organisms’ abilities to reproduce were also unaltered. While this study only examined the biosolids from one mill, there is the potential that land-application of characteristically well-defined pulp mill biosolids may constitute an acceptable way of disposing of pulp and paper mill biosolid residues. However, the biosolids coming from different mills, with differing processes, must be dealt with on a case-by-case situation. Each series of biosolids must be rigorously tested for toxicological impact in the laboratory under tightly controlled conditions. Subsequently, field experimentation must be conducted before definitive conclusions can be made.