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In recent decades, there has been a growing interest in the recycling of organic materials such as paper mill biosolids (PB) and biochar for use as soil amendments. However, the benefits of co-application of PB and biochar and its effects on soil phosphorus (P) availability remain unknown. An incubation study was conducted on two acidic soils to assess the effect of two PB types (2.5% w/w) co-applied with three rates (0%, 2.5%, and 5% w/w) of pine (Pinus strobus L.) biochar on soil P fractions. An unfertilized control and a mineral NP fertilizer were used as a reference. Soil P fractions were determined by Hedley procedure after 2 and 16 wk of incubation. Material fractionation indicated that the PB containing the highest total P and the lowest Al content had the highest proportion of labile P, whereas most P in the biochar was in a stable form. The incubation study revealed that the P-rich PB increased P availability in both soils to a level comparable to mineral fertilizer at the end of the incubation. The addition of biochar to PB, however, did not affect soil P availability, but the highest rate induced a conversion of P fixed to Al and Fe oxides towards recalcitrant forms, particularly in the sandy loam soil. We conclude that co-applying biochar and PB could be more beneficial than application biochar alone and soils amended with such a mixture would be expected to release part of their P slowly over a longer period of time.

Amending croplands with forest residues may help in restoring soil properties in fields subject to intensive land management. Despite their known benefits when applied separately, co-application of wood biochar with paper mill biosolids (PB) has seen little investigation under field conditions. A study was initiated in Québec, QC, Canada, to determine the effect of a single application of wood biochar with and without PB on the nitrogen (N) and phosphorus (P) availability of two pH-neutral to alkaline loamy soils. Biochar at 0, 10, and 20 Mg dry weight·ha−1 and PB at 30 Mg wet weight·ha−1 were applied before planting of corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] in 2018. Residual effect of this co-application was determined under soybean and corn in the subsequent year. In both years, corn received supplemental N and P from mineral fertilizers according to local agronomic recommendations. Co-applying biochar and PB reduced soil NO3-N availability in the year of application and decreased corn yield by 1.0 Mg·ha−1 compared with biochar or PB applied alone, but these amendments did not affect soybean yields. In the following year, the previous biochar addition increased soybean yield by 0.6 Mg·ha−1 but had little effect on corn. For both years, biochar addition induced a large increase in soil Mehlich-3 P. This study revealed that wood biochar positively impacted P status of these soils but was not a source of N to crops even when co-applied with PB.

Acidification and metal mobility may present challenges in soil receiving paper mill biosolids (PB). Co-applying biochar and PB could help prevent these issues, but its effect must be assessed. The objective of this 224 d incubation study was to evaluate the effect of amending two acidic soils, a clay and sandy loam, with two PB types varying in pH (PB1, pH = 7.80; and PB2, pH = 4.51) co-applied with three rates (0%, 2.5%, and 5% w/w) of pine (Pinus strobus L.) biochar on soil pH and macro- (P, K, Ca, and Mg) and micronutrients (Cu, Zn, Fe, and Mn). In both soils, co-applying biochar and PB significantly increased soil pH and extractable K concentration compared with PB-only application, whereas amending with PB significantly increased soil extractable P concentration compared with the unamended soil. In comparison with PB only, co-applying 5% biochar and PB decreased extractable Cu concentration in both soils and extractable Fe concentration in the sandy loam soil. This study showed that co-applying biochar and PB can be more beneficial to agricultural soils than application of PB alone by supplying nutrients and helping prevent metal toxicity by raising pH, especially in acidic sandy soils.

Combined paper mill biosolids (PB) are a well-known fertilizing source of nitrogen (N) and phosphorus (P). Many jurisdictions have established default values for estimating their agronomic N and P contribution, but nutrient release can vary with their chemical properties, and this has been little studied. The objective of this incubation study was to compare four PB of different sources along with a de-inking paper sludge (DPS) for their N and P release in three contrasting soils under controlled conditions (25 °C, 60% water-filled pore space). Treatments consisted of PB or DPS at 50 Mg fresh mass ha−1, PB at 30 Mg fresh mass ha−1 plus inorganic N to supply 100 kg available N ha−1, inorganic NP fertilizer, and an unfertilized control. Measurements of NO3 + NH4-N were made after 3 d and 1, 2, 3, 4, 6, 8, 12, and 16 wk of incubation. Mehlich-3 P was measured after 2 and 16 wk of incubation. Nitrogen mineralization generally declined a few days after PB addition and then gradually and constantly increased. The P mineralization of PB also increased with time. By the end of incubation, net N and P release averaged 30% (7%–49%) and 75% (16%–116%) of the NP fertilizer, respectively. The intensity of release, however, varied with material characteristics and soil type. Mineral N addition to the 30 Mg PB ha−1 promoted N release to a level comparable to NP fertilizer. Soil N immobilization occurred with the DPS application. Current default N value used for PB in Quebec and Ontario is appropriate but not P.

Over 50 years ago, a marine estuary was converted to a wastewater stabilization basin for treatment of primarily pulp and paper effluent. As a result, the basin was immediately converted to a “freshwater” environment and subsequently accumulated a thin layer of black, organic-rich sediment containing varying amounts of dioxins and furans, metals, polycyclic aromatic hydrocarbons, and petroleum hydrocarbons. Previous studies on the site have shown that the majority of this contamination in the basin appears to have been contained within this black sediment layer and not migrated to any significant extent into the original underlying marine sediments. The purpose of this study is to examine sediment porewater chemistry changes that have occurred over 51 years of operation of the stabilization basin with the intent of better understanding why contamination has been minimal into the underlying natural marine sediments. Field and laboratory testing is presented to characterize the physical, chemical, and mineralogical sediments in the basin. Porewater chemistry profiles obtained from this work are then used in combination with a one-dimensional contaminant transport model to examine the role of diffusion, sorption, and upward groundwater flux in the porewater profiles found for the sediments.

Paper mill biosolids (PB) are recognized as a valuable source of carbon for the physical improvement of arable soils. However, little is known about the composition of carbohydrates of these materials and their breakdown in soil, which contributes to soil structural stability. The objectives of this study were to characterize the carbohydrates in PB and to determine under controlled conditions and in the field the soil carbohydrate content and water-stable aggregation. The field experiment consisted of PB applied every year (2000–2008) at 0, 30, and 60 Mg wet weight·ha−1 to annual row crops with soils collected after 3, 6, and 9 yr. The other experiment consisted of PB added at 50 Mg wet weight·ha−1 to two soils, a clay and a sandy loam, and incubated at 25 °C and 60% water-filled pore space for 16 wk. The PB differed in their content in galactose, mannose, and arabinose for total fraction and sum of carbohydrates for water-soluble fraction. In the field, repeated annual PB application increased most of soil total carbohydrates (sum and individuals) after 3 yr and the proportion of >1 mm stable aggregates. The incubation study confirmed results obtained in the field, where the PB richest in carbohydrates induced the highest increases in soil total carbohydrates in both soil types. Soil total and microbial (galactose and mannose)-derived carbohydrates were closely correlated with the percentage of large aggregates, while with water-soluble carbohydrates, they are highly correlated to the amount of microbial carbohydrates applied, thus further contributing to improve soil C quality.

A novel, simple, and low-cost spray painting technique has been developed for the fabrication of microfluidic paper-based devices. The devices that we developed utilize aerosol spray paint to build hydrophobic barriers and employ a hole puncher to obtain paper-based patterned layers and paper dots without using any specialized instruments (e.g., without a laser cutter). The entire manufacturing process is extremely simple, inexpensive, and rapid, which means that it can be applied broadly. Furthermore, the application of the device to iron detection was demonstrated. A linear relationship between the colour value and the iron concentration was observed from 0 to 0.02 g/L. The developed microfluidic paper-based device for iron detection exhibited a low detection limit (0.00090 g/L), good selectivity, and acceptable recovery.