Enhancement of Solubility and Biohydrogen Production from Sewage Sludge with Lime Mud Filtrate

This work has been performed to investigate the use of lime mud filtrate (LMF) pretreatment to enhance hydrogen (H₂) evolution from sewage sludge (SS). The SS samples were pretreated with LMF (pH 8.0–11.0) at 55 °C for 48 h, prior to the H₂ fermentation. The maximum H₂ yield of 38.30 ml/g-VS (volatile solid) was obtained from the SS pretreated by LMF pH of 10.0, with the corresponding lag time of 3.10 h, which was well described by the modified Gompertz model. Adequate pH of LMF facilitated the solubilization of SS and the release of organic matters, providing adequate substrates for subsequent bio-H₂ evolution. The soluble chemical oxygen demand was increased from 25.0 to 91.7%, as compared with the control test without LMF soak. However, further increase in pH of LMF could decrease the concentration of available substrate, thus reducing the H₂ yield. This technique revealed sustainable waste management and energy recovery.     

大型沼气工程生态应用关键技术研究

本文系统分析了大型沼气工程整个能量与物质循环过程的几个关键环节,包括原料的收集、原料配制与预处理、厌氧消化、好氧水处理、沼气的净化贮存和输送以及沼渣、沼液无害化处理及其在农作物上的施用等.将收集好的原料先进行短化和去杂处理,按照一定的条件再进行配制;配好以后选择适宜的发酵条件在消化器中进行厌氧消化产生沼气;沼气产生以后必须设法脱除沼气中的水和H2S,水脱除通常采用脱水装置进行,H2s的脱除通常采用脱硫塔,内装脱硫剂进行脱硫.试验表明,沼渣与沼液有促进作物生长、提高作物品质、增强作物抵抗病虫害的功用.     

Kinetic and Thermodynamic Studies of Chlorinated Organic Compound Degradation by Siderite-Activated Peroxide and Persulfate

The efficacy of two oxidant systems, iron-activated hydrogen peroxide (H₂O₂) and iron-activated hydrogen peroxide coupled with persulfate (S₂O₈ ^2?), was investigated for treatment of two chlorinated organic compounds, trichloroethene (TCE) and 1,2-dichloroethane (DCA). Batch tests were conducted at multiple temperatures (10–50 °C) to investigate degradation kinetics and reaction thermodynamics. The influence of an inorganic salt, dihydrogen phosphate ion (H₂PO₄ ^?), on oxidative degradation was also examined. The degradation of TCE was promoted in both systems, with greater degradation observed for higher temperatures. The inhibition effect of H₂PO₄ ^? on the degradation of TCE increased with increasing temperature for the iron-activated H₂O₂ system but decreased for the iron-activated hydrogen peroxide-persulfate system. DCA degradation was limited in the iron-activated hydrogen peroxide system. Conversely, significant DCA degradation (87% in 48 h at 20 °C) occurred in the iron-activated hydrogen peroxide-persulfate system, indicating the crucial role of sulfate radical (SO₄ ^??) from persulfate on the oxidative degradation of DCA. The activation energy values varied from 37.7 to 72.9 kJ/mol, depending on the different reactants. Overall, the binary hydrogen peroxide-persulfate oxidant system exhibited better performance than hydrogen peroxide alone for TCE and DCA degradation.     

Removal of H2S by Metal Ferrites Produced in the Purification of Metal-Bearing Waste Water. Study of the Reaction Mechanism

Waste water polluted with heavy metals can besuccessfully purified by precipitation of the metals from analkaline solution containing iron (II), giving rise to aferrite sludge. The solid metal ferrites obtained in thismanner can be used to remove hydrogen sulphide from a gasstream. Based on a Taguchi experimental design, ferrite solidparticle and pore size, and the temperature resulting inmaximum retention of H₂S by the solid were optimised.Under the optimum conditions, predicted by the method, eachgram of ferrite was able to retain 0.274 g H₂S.In addition, a ferrite containing a known lead concentration,obtained by the precipitation method under optimal conditionsof pH, temperature and Fe/Pb ratio, was used to study theexothermic H₂S retention reaction. The chemical reactionoccurring between the ferrite and the H₂S wasinvestigated by characterisation of the compounds before(Pb_0.04Fe^II _0.96 Fe^III ₂O₄·nH₂O solids composed ofPb_xFe_3-xO₄, magnetite Fe₃O₄ andhydrated lead oxide PbO_n·H₂O) and after (PbS, PbSO₄, S, FeS₂ and α-FeO(OH)) the retention process.     

Evaluation of Magnetic Coagulant (α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-MO) and its Reuse in Textile Wastewater Treatment

The textile industries are characterized as one of the biggest consumers of potable water and chemical products throughout its process, being responsible for the elevated wastewater generation with intense coloration and wide polluting potential. In this context, the present study proposes the development and application of a new coagulant material for textile wastewater treatment. The proposed coagulant (α-Fe₂O₃-MO) was composed by hematite nanoparticles (α-Fe₂O₃) obtained by a simple non-pollutant methodology, associated with Moringa oleifera (MO) seeds saline extract compounds. Coagulation/flocculation (CF) efficiency was evaluated by removal of physicochemical parameters such as apparent color, turbidity, and compounds with absorption at UV_254nm (UV_254nm) through CF tests carried out on Jar test equipment and sedimentation carried out in the presence and absence of external magnetic field (600 k Am^?1). Kinetics sedimentation was from 0 to 90 min. The use of this new coagulant allowed the removal of 92.37% for apparent color, 91.43% for turbidity, and 46.09% for UV_254nm, indicating that the proposed coagulant association was efficient in the treatment of this type of wastewater under external magnetic field with only 10 min of sedimentation. In addition, the resulting sludge from CF process was tested as base material for a new coagulant synthesis, demonstrating great reuse potential. Therefore, the new proposed coagulant, composed of α-Fe₂O₃ and the compounds present in the seed extract of MO, has applicability for textile wastewater treatment demonstrating high removal rate for all evaluated parameters with cost reduction in the proposed treatment for this wastewater.     

Effects of Low-Level Aqueous Hydrogen Sulfide and Other Sulfur Species on Lettuce (Lactuca sativa) Seed Germination

Low concentrations of aqueous hydrogen sulfide (H₂S) can stimulate growth of some crops. However, it is not clear whether H₂S provides crops with only sulfur and whether other sulfur compounds have similar beneficial effects. Therefore, impacts of solutions of sodium sulfate (Na₂SO₄), sodium sulfite (Na₂SO₃), sodium sulfide (Na₂S), ferrous sulfide (FeS), and H₂S at 0.01–1 mM were assessed on 5-day lettuce seed germination. Results showed that 0.01 mM H₂S solution significantly increased lettuce shoot elongation by 40 percent (to 43.6 mm from 31.0 mm in the control), whereas 0.1 mM increased elongation by 24 percent to 38.5 mm. Only a slight 10 percent increase was observed in 0.1 mM Na₂SO₄, suggesting that ameliorative impact of H₂S on plant growth was not a result of providing sulfur nutrient. Other sulfur solutions, however, inhibited lettuce germination and elongation to varying extents, hinting that H₂S might work as a signal molecule in regulating plant cellular activities.     

Phosphorus Characterisation of Sludge and Crust Produced by Stabilisation Ponds in a Dairy Manure Management System

In dairy farming, recirculation and continuous use of nutrients are necessary for sustainable nutrient management in both the short- and long-term. When managed effectively, nutrient recycling can improve soil fertility. On the other hand, if applied nutrients are in excess of the soil’s nutrient holding capacity, nutrients can enter surface and ground water bodies resulting in eutrophication. Phosphorus (P) characterisation in manure, pond sludge and crust, in terms of plant availability, is the first step to sustainably manage nutrients within dairy farms. In this study, pond sludge and crust were characterised for P using a sequential fractionation method. Pond sludge and crust contained significant amounts of labile P. Water extractable P (H₂O-P) in primary anaerobic pond and secondary facultative pond sludges was found to be about 8 to 13 times higher than the amount found in the surface soil (0–10 cm) of a grazing paddock. Similarly, sodium bicarbonate extractable P (NaHCO₃-P) in the two types of sludges was found to be about 6 times higher than in the soil. The relatively higher labile P (H₂O-P and NaHCO₃-P) in sludge compared to soil indicates that the sludge can be utilised as a P fertilizer on grazing pasture. In contrast, lower H₂O-P compared to that of raw manure indicates that the use of sludge and crust instead of raw manure can reduce the possibility of P loss by surface runoff and leaching. Hence, it is preferable to use pond sludge and crust as fertiliser instead of raw manure.     

Relationship Between Sulphate Starvation and Chromate Reduction in a H2-fed Fixed-film Bioreactor

While developing a low-sulphate system combining indirect chromate-reduction by biologically-produced hydrogen sulphide and direct biological chromate-reduction to treat chromate-bearing waters, the aim of the present work was to evaluate the influence of sulphate and H₂ starvation on chromate reduction. Chromate-reduction was performed under continuous-feed conditions in a fixed-film column bioreactor originally inoculated with a bacterial consortium containing Desulfomicrobium norvegicum, and fed with H₂. With 500 mg l^?1 of sulphate in the feed solution, total chromate-reduction was observed in the effluent whereas sulphate-reduction was strongly decreased, as also confirmed by measurements of isotopic ratios for sulphur. In the absence of sulphate, a chromate-reduction activity was still observed but was lower than in the presence of sulphate, and chromate-reduction was H₂-dependent. Molecular biology techniques revealed the composition of the bacterial population in the effluent. D. norvegicum together with other micro-organisms of the Bacteria domain were detected. They include members related to the genera Acinetobacter, Acetobacterium and Rhodocyclus. Even when sulphate-reduction was strongly decreased, the presence of sulphate enhances the efficiency of the H₂-dependent chromate-reduction. A H₂- and CO₂-consuming bacterial population may be used in a globally autotrophic process to reduce chromate at low sulphate concentration, thus avoiding excess sulphide production.     

Summer green-manuring crops and zinc fertilization on productivity and economics of basmati rice (Oryza sativa L.)

Field experiments were conducted to study the effects of summer green-manuring crops and zinc (Zn) fertilization on the productivity and economics of Basmati rice. Sesbania aculeata summer green-manuring crop residue incorporation (SGMI) gave highest values of all the growth and yield attributes, grain and straw yield, viz. 3.58, 3.69 t ha^?1 and 16.14, 16.25 t ha^?1 of Basmati rice in 2008 and 2009. Among the Zn fertilization treatments, application of 2.0% Zn-enriched urea (ZEU) as ZnSO₄ · H₂O significantly influenced yield attributes and yield of Basmati rice during both years, and the increase in grain yield was 38.5 and 40.0% over absolute control (no N and no Zn) and 11.9 and 13.6% over control (only N) in both years of study. However, 2.0% ZEU (ZnO) was very close in terms of yield attributes and grain, straw yields of Basmati rice. As regards to the economics of Basmati rice, SGMI and 2.0% ZEU (ZnSO₄ · H₂O) Zn fertilization treatments gave the highest gross (SGMI, 85,985 and 91,582 INR ha^?1; 2.0% ZEU, 89,837 and 59,851 INR ha^?1) and net (SGMI, 56,997 and 61,445 INR ha^?1; 2.0% ZEU, 59,851 and 64,442 INR ha^?1) returns, respectively, compared with incorporation of the remaining summer green manuring residue and Zn fertilization treatments in 2008 and 2009. A significantly higher benefit:cost ratio was recorded with SGMI and 2.0% ZEU (ZnSO₄ · H₂O). Overall, Sesbania aculeata green manuring and 2.0% ZEU (ZnSO₄ · H₂O) are excellent sources of N and Zn for improved productivity of Basmati rice.     

Development of a Biofilter with Tire-Derived Rubber Particle Media for Hydrogen Sulfide Odor Removal

The biofilter system containing tire-derived rubber particle (TDRP) filter media was utilized to treat the odorous gas contaminant, hydrogen sulfide, in consideration of the economic advantage of reusing discarded tire materials and the high potential of TDRP media for biofilm attachment. The pilot-scale system having 0.38 m³ of bed volume operated with synthetic hydrogen sulfide gas on continuous basis from a range of 0.34 to 1.15 m³/min. This bioreactor system achieved over 94% removal efficiency at 20?C90 ppm of inlet H₂S concentration while operating in 20?C67 s of empty bed retention time, indicating that overall effective operation was performed at mass loading rates of H₂S ranging from 19.6 to 28.5 g H₂S/(m³?h). It was apparent by the effectiveness of the system??s performance that this system had the capability to effectively remove hydrogen sulfide with high efficiency over a range of concentrations. A maximum elimination capacity was not found for the biofilter during this study, which tested loading rates between 0 and 30 g H₂S/(m³?h).     

Technical and Economical Assessment and Extrapolation of a 200-dm3 Pilot Bioreactor for Reduction of Sulphate and Metals in Acid Mine Waters

Acidity, presence of metals and high-sulphate concentration are typical characteristics found in acid mine waters (AMWs). A 200-dm³ pilot, allowing bacterial conversion of sulphate into sulphide, was designed to treat AMWs. A fixed-bed column was filled with pozzolana, inoculated with a bacterial population containing the sulphate-reducing organism Desulfomicrobium norvegicum and fed with a H₂ and CO₂ gas mixture. The pilot worked in continuous-feeding conditions during 36 days. An actual AMW was sequentially treated by neutralisation of acidity, precipitation of metals using sulphide produced by the bioreactor and bioconversion of sulphate in the bioreactor fed with the sulphide-treated effluent. The residence time in the bioreactor was decreased down to 8.5 h. The sulphate reduction rate, correlated with the temperature between 5 and 17°C, varied between 35 and 95 mg dm^?3 h^?1. On the basis of the technical assessment previously made and after setting up some extrapolation hypotheses and calculations for a 10 m³ h^?1 unit, the treatment cost per cubic meter of AMW was evaluated.     

Labile water soluble components govern the short-term microbial decay of hydrochar from sewage sludge

Due to higher proportions of labile carbon (C) compounds the suitability of biochar produced by hydrothermal carbonization (HTC) for C sequestration is questionable. We hypothesized that pre-treatment with water would reduce the biological decay of hydrochar from sewage sludge. Unwashed and washed feedstock and hydrochar were incubated in a short-term experiment. The kinetics of the biological decomposition of the materials was calculated on the basis of a double exponential model and the C sequestration potential using the CANDY Carbon Balance (CCB) model. Biological decomposition of the carbonized materials was governed by the percentage of labile C compounds. Mean residence time of a fast (MRT_fast) and slow decay pool (MRT_slow) of unwashed hydrochars varied clearly (MRT_fast: 0.8 – 5.0 months and the MRT_slow: 5.0–18.6 months). The pre-treatment with water removed labile hydrochar C and reduced the biological accessibility. MRT_fast and MRT_slow was increased by intensive washings (MRT_fast: 5.0–7.4 months and the MRT_slow: 14.9 months). High synthesis coefficients suggest that hydrochar C was humified and transferred into stabilized SOC. The results clearly show that once adsorbed components were eliminated, and as compared to pyrolysed biochar hydrochar from sewage sludge may also be useful for soil C sequestration.     

EFFECTS OF CALCIUM ON LIGNIFICATION RELATED PARAMETERS IN SODIUM CHLORIDE-STRESSED SOYBEAN ROOTS

The effects of exogenous calcium (Ca²⁺) on root growth and lignification-related parameters – phenylalanine ammonia-lyase (PAL) and peroxidases (POD) activities, hydrogen peroxide (H₂O₂) and lignin contents – in roots of NaCl-stressed soybean seedlings were analyzed. Three-day-old seedlings were cultivated in half-strength Hoagland's solution (pH 6.0) with or without 5 mM calcium nitrate [Ca(NO₃)₂] and 50 to 200 mM sodium chloride (NaCl) in a growth chamber (25°C, 12/12 h light/dark photoperiod, irradiance of 280 μmol m^?2 s^?1) for 24 h. In general, results showed that the absence of Ca²⁺ reduced root growth and increased lignification of soybean seedlings grown in NaCl-free nutrient solution. NaCl reduced the root growth and all lignification-related parameters. Root growth, PAL and POD activities and hydrogen peroxide (H₂O₂) contents were more affected after NaCl treatments without Ca²⁺ in the nutrient solution. At 5 mM, Ca²⁺ did not alleviate the deleterious effects of NaCl on lignification-related parameters.     

Characteristics of Biochemical and Fractal Structure of Activated Sludge with Thermochemical Lysis

In this study, we investigated the structural characteristic and biochemical properties of waste-activated sludge after thermochemical pretreatment. The results show that with the increase dosage of hydrochloric acid or sodium hydroxide, the concentration of suspended solid (SS) and volatile suspended solids (VSS) declined, especially at pH 12 + H (“H” means heating). At the same time, soluble chemical oxygen demand (SCOD) all increased as well, especially at pH 12, the greatest lysis effect appeared. Protein and polysaccharide presented a similar law with SCOD. Furthermore, the specific surface area (SSA), two-dimensional fractal dimension (D ₂), and three-dimensional fractal dimension (D ₃) all increased to a certain degree with acid/alkali pretreatment whether or not heating. Otherwise, the median particle size (d _0.5) and zeta potential decreased leading to more compact and stable floc structure and reduction effect compared with the original sludge. In Pearson correlation analysis, SSA and SS, SSA and VSS, zeta potential and SCOD, and zeta potential and protein have significant negative correlations; D ₃ and SSA have a significant correlation with SS, VSS, SCOD, and protein. Consequently, measuring the structural parameters D ₃ and SSA online can reflect the effects of sludge lysis indirectly, which will be helpful to guide the practical application.     

Crop Utilization of Nitrogen in Swine Lagoon Sludge

Swine lagoon sludge is commonly applied to soil as a source of nitrogen (N) for crop production but the fate of applied N not recovered from the soil by the receiver crop has received little attention. The objectives of this study were to (1) assess the yield and N accumulation responses of corn (Zea mays L.) and wheat (Triticum aestivum) to different levels of N applied as swine lagoon sludge, (2) quantify recovery of residual N accumulation by the second and third crops after sludge application, and (3) evaluate the effect of different sludge N rates on nitrate (NO₃-N) concentrations in the soil. Sludge N trials were conducted with wheat on two swine farms and with corn on one swine farm in the coastal plain of North Carolina. Agronomic optimum N rates for wheat grown at two locations was 360 kg total sludge N ha^?1 and the optimum N rate for corn at one location was 327 kg total sludge N ha^?1. Residual N recovered by subsequent wheat and corn crops following the corn crop that received lagoon sludge was 3 and 12 kg N ha^?1, respectively, on a whole-plant basis and 2 and 10 kg N ha^?1, respectively, on a grain basis at the agronomic optimum N rate for corn (327 kg sludge N ha^?1). From the 327 kg ha^?1 of sludge N applied to corn, 249 kg N ha^?1 were not recovered after harvest of three crops for grain. Accumulation in recalcitrant soil organic N pools, ammonia (NH₃) volatilization during sludge application, return of N in stover/straw to the soil, and leaching of NO₃ from the root zone probably account for much of the nonutilized N. At the agronomic sludge N rate for corn (327 kg N ha^?1), downward movement of NO₃-N through the soil was similar to that for the 168 kg N ha^?1 urea ammonium nitrate (UAN) treatment. Thus, potential N pollution of groundwater by land application of lagoon sludge would not exceed that caused by UAN application.     

SE—Structures and Environment: Effects of Solids Separation and Time on the Production of Odorous Compounds in Stored Pig Slurry

Fresh pig faeces were separated into seven different liquid portions with particle size ranges <2·0, <1·4, <1·0, <0·5, <0·25, <0·15, and <0·075 mm, respectively. Separation was achieved by consecutive sieving of the fresh pig manure through a series of seven American Society for Testing Materials (ASTM) standard wire screen sieves with openings of 2·0, 1·4, 1·0, 0·5, 0·25, 0·15 and 0·075 mm. The separated manure fractions were stored at an ambient temperature of approximately 20°C in Plexiglas columns (91 cm deep and 15 cm in diameter) to simulate storage in under-floor or in other types of holding pits. The results indicated that although solid–liquid separation was found to reduce production of volatile fatty acids (VFAs) and 5-day biochemical oxygen demand (BOD₅) regarded as odour precursors, this technique might not significantly reduce odour nuisances from swine facilities unless particles smaller than 0·075mm are separated from the liquids. Inverse linear correlations were observed between total solids (TS) and total volatile solids (TVS) with both BOD₅and VFAs and therefore their respective levels could also be used to quantify the potential of odour nuisances in stored pig manure.     

Leaching of Metals from Oxidising Sulphide Mine Tailings with and without Sewage Sludge Application

A 20-month column experiment investigated leaching of Al, Cu, Mn, Ni, Zn, Cd and Pb during sulphide oxidation in mine tailings with and without sewage sludge (SS) amendment. Leachate pH decreased gradually in all columns during the experiment, irrespective of treatment, due to sulphide oxidation. As the degree of sulphide oxidation, and thus the pH trajectory, differed between replicates (n?=?3), running data for each column used are reported separately and the relationships between sulphide oxidation, metal leaching and treatment in each column compared. Mean pH in the columns correlated negatively with total amounts of leached SO₄ ^2-. In the beginning of the experiment the leachate concentrations of Al, Cu, Zn, Ni and Pb were higher in SS-treated columns due to high initial concentrations of dissolved organic carbon. As leaching proceeded, however, the amounts of Al, Cu, Mn and Ni leached from the columns were closely related to the degree of sulphide oxidation in each column, i.e. to its mean pH. There were no statistically significant differences between treatments regarding the total amounts of metals leached and thus addition of sewage sludge to the tailings appeared to play a minor role for metal leaching patterns. Peak concentrations of Al and Cu in the leachate from untreated tailings and of Zn in the leachate from both untreated and SS-treated tailings at pH 4 exceeded national background values for groundwater.     

Mineralisation of Surfactants Using Ultrasound and the Advanced Fenton Process

The destruction of the surfactants, sodium dodecylbenzene sulfonate (DBS) and dodecyl pyridinium chloride (DPC), using an advanced oxidation process is described. The use of zero valent iron (ZVI) and hydrogen peroxide at pH = 2.5 (the advanced Fenton process), with and without, the application of 20 kHz ultrasound leads to extensive mineralisation of both materials as determined by total organic carbon (TOC) measurements. For DBS, merely stirring with ZVI and H₂O₂ at 20°C leads to a 51% decrease in TOC, but using 20 kHz ultrasound at 40°C, maintaining the pH at 2.5 throughout and adding extra amounts of ZVI and H₂O₂ during the degradation, then the extent of mineralisation of DBS is substantially increased to 93%. A similar result is seen for DPC where virtually no degradation occurs at 20°C, but if extra amounts of both ZVI and hydrogen peroxide are introduced during the reaction at 40°C and the pH is maintained at 2.5, then an 87% mineralisation of DPC is obtained. The slow latent remediation of both surfactants and the mechanism of degradation are also discussed.     

Hydraulic Retention Time Influence on Improving Flocculation in the Activated Sludge Processes Through Polyelectrolytes

Hydraulic retention time (HRT) influence improving sludge flocculation with adding the polyelectrolytes (non-ionic, anionic, and cationic) was studied on an activated sludge (AS) system fed with synthetic domestic wastewater (SDW), dairy industry wastewater (DIW), and caramel industry wastewater (CIW). The sludge volumetric index, food/microorganism ratio (F/M), and mixed liquor volatile suspended solids at different HRTs (6, 8 and 10 h) were monitored on an experimental model. Results showed that both SDW and IW had the best sludge flocculation conditions at 8 h and 100 mL of non-ionic polyelectrolyte (0.2 mg L^?1). In addition, this phenomenon reached the organic matter removal efficiencies of 95.9, 95.7, and 94.2% for SDW, DIW, and CIW, respectively. Therefore, optimum HRT increased the organic matter removal efficiencies by 10%, sludge concentration by 37% (22–55%), and F/M ratio by 70%. Moreover, the polyelectrolytes used in AS improved the sludge flocculation by 2.9 times.     

Mercury Partitioning in Surface Sediments of the Upper St. Lawrence River (Canada): Evidence of the Importance of the Sulphur Chemistry

An intensive survey of mercury speciation was performed at a site on the Upper St. Lawrence River near Cornwall, Ontario, Canada with a history mercury contamination in sediments. Surface sediments were collected every 1.50 h. Total mercury (Hg_total), methylmercury (MeHg), organic carbon, inorganic and organic sulphur were determined in the solid fraction. Dissolved Hg_total, MeHg and dissolved organic carbon (DOC) were measured in pore waters. Concentrations of Hg_total in the upper layers (first 5 cm) were high, ranging from 1.42 to 25.8 nmol g^?1 in solids and from 125 to 449 pM in pore waters. MeHg levels were also high, ranging from 4.34 to 34.1 pmol g^?1 in solids and from 40 to 96 pM in pore waters. This amounts to up to 1.4% of Hg_total present as MeHg in solids and 64% in pore waters. A daily pattern for Hg_total was observed in the solid fraction. The MeHg distribution in solids and pore waters was not correlated with Hg_total or DOC_, suggesting that the concentrations of MeHg are probably more influenced by the relative rates of methylation/demethylation reactions in the sediment–water interface. Acid volatile sulphide levels and DOC were inversely correlated with organic sulphur (S_org) levels suggesting that both parameters are involved in the rapid production of S_org. A positive correlation was also observed between Hg_total and S_org in solids (R?=?0.87, p?<?0.01) illustrating the importance of organic sulphur in the retention and distribution of Hg in the solid fraction of the sediments. The results suggest that variations of Hg_total concentrations in Upper St. Lawrence River surface sediments were strongly influenced by the formation/deposition/retention of organic sulphur compounds in the sediment–water interface.