The High Arctic glacial ecosystem: new insights from nutrient budgets

This paper describes detailed budgets of water, Cl⁻, dissolved Si and both inorganic and organic forms of nitrogen and phosphorus for two small glacier basins in Arctic Svalbard (Midre Lovénbreen and AustreBrøggerbreen). Rates of nutrient deposition are modest, dominated by inorganic nitrogen and episodically enhanced by extreme events. Hence deposition rates are also variable, ranging from 20 to 72 kg NO₃-N km⁻² a⁻¹ and 10–37 kg NH₄-N km⁻² a⁻¹ over just two consecutive years. Deposition of dissolved organic and particulate forms of nitrogen (DONand PN respectively) also appears significant and therefore requires further investigation (3–8 kg DON-N km⁻² and 7–26 kg PN-N km⁻² during winter – no summer data are available). Evidence for microbially mediated nutrient cycling within the glacial system is clear in the nutrient budgets, as is the release of large phosphorus, Si and organic/particulate nitrogen fluxes by subglacial erosion. The latter is entirely dependent upon the presence of subglacial drainage, promoting silicate mineral dissolution and the erosion of largely unweathered apatite. The large DON and PN fluxes are surprising and may relate to young organic nitrogen associated with microbial life within the glaciers. This is because wide spread assimilation of NH₄⁺ and perhaps even nitrification occurs on the glacier surface, most likely within abundant cryoconite holes. Further microbial activity also occurs at the glacier bed, where denitrification and sulphate reduction is now known to take place. Thus a two component ‘glacial ecosystem’ is proposed that is highly sensitive to climate change.     

Denitrification kinetics of simulated fish processing wastewater at different ratios of nitrate to biomass

Denitrification was studied in anoxic batch cultures of a simulated fish processing wastewater at 37 r C and pH 7.5, using a denitrifying enrichment culture from fishery wastewater. Different initial nitrate to biomass ratios (So/Xo) were used: nitrate and biomass varied from 7.5 to 94.7 mg NO₃-N l^–1, and from 20 to 4300 mg volatile suspended solids l^–1, respectively. The specific maximum denitrification rate (r _m) and the cell yield (Y _{X / S}) depended on the So/Xo ratio under anoxic conditions: r _m increased from 1.2 to 1584 mg NO₃-N g^–1 VSS h^–1 and Y _{X / S} decreased from 42 to 0.03 mg VSS mg^–1 NO₃-N when So/Xo varied from 5.5 10^{– 3} to 9.3 mg NO₃-N/mg VSS. Nomenclature C_{NO3 – N} nitrate concentration, mg NO₃-N l^–1 K _S saturation constant, mg NO₃-N l^–1 r _m specific maximum denitrification rate, mg NO₃-N g^–1 VSS h^–1 So initial substrate concentration, mg l^–1 t time, h TOC total organic carbon VSS volatile suspended solids x biomass concentration, g VSS l^–1 Xo initial biomass concentration, g VSS l^–1 Y _X/S substrate to biomass cell yield, mg VSS/mg N Greek symbols: _m maximum specific growth rate of the anoxic microbial population, 1 h^–1     

Effects of prolonged cycle ergometer exercise on maximal muscle power and oxygen uptake in humans

The mechanical power (W_tot, W·kg^–1) developed during ten revolutions of all-out periods of cycle ergometer exercise (4–9 s) was measured every 5–6 min in six subjects from rest or from a baseline of constant aerobic exercise [50%–80% of maximal oxygen uptake (VO_2max)] of 20–40 min duration. The oxygen uptake [VO₂ (W·kg^–1, 1 ml O₂ = 20.9 J)] and venous blood lactate concentration ([la]_b, mM) were also measured every 15 s and 2 min, respectively. During the first all-out period, W_tot decreased linearly with the intensity of the priming exercise (W_tot = 11.9–0.25·VO₂). After the first all-out period (i greater than 5–6 min), and if the exercise intensity was less than 60% VO_2max, W_tot, VO₂ and [la]_b remained constant until the end of the exercise. For exercise intensities greater than 60% VO_2max, VO₂ and [la]_b showed continuous upward drifts and W_tot continued decreasing. Under these conditions, the rate of decrease of W_tot was linearly related to the rate of increase of V [(d W_tot/dt) (W·kg^–1·s^–1) = 5.0·10^–5 –0.20·(d VO₂/dt) (W·kg^–1·s^–1)] and this was linearly related to the rate of increase of [la]_b [(d VO₂/dt) (W·kg^–1·s^–1) = 2.310^–4 + 5.910^–5·(d [la]_b/dt) (mM·s^–1)]. These findings would suggest that the decrease of W_tot during the first all-out period was due to the decay of phosphocreatine concentration in the exercising muscles occurring at the onset of exercise and the slow drifts of VO₂ (upwards) and of W_tot (downwards) during intense exercise at constant W_tot could be attributed to the continuous accumulation of lactate in the blood (and in the working muscles).     

Ammonium uptake in alpine streams in the High Tatra Mountains (Slovakia)

Uptake of NH _inf4 ^sup+ -N by streambed biota of mountain brooks was studied in the alpine zone of the High Tatra Mountains. Experiments were performed involving in situ dosing of ammonium directly to the acidified stream and incubations of ammonium and streambed bryophytes in enclosures within a range of pH from 4.45 to 8.10.NH _inf4 ^sup+ -N uptake length decreased with decreasing stream discharge, while comparable values of discharge-normalized uptake lengths were found during two in situ experiments.Maximum uptake rates of NH _inf4 ^sup+ -N obtained during the incubation of bryophytes (6 to 11 mg m^–2 h^–1) were comparable with results of two in situ experiments (8 and 12 mg m^–2 h^–1). The average NH _inf4 ^sup+ -N uptake rates observed during incubations lasting 3 to 5 hours (4.3 mg m^–2 h^–1) were not related to the pH of stream water. Nitrification of about 50% of the NH _inf4 ^sup+ -N added was observed in non-acidified streams, but was negligible in acidified streams. Significant photoinhibition of nitrification was observed in non-acidified streams during enclosure experiments.     

Effects of forest clear-cutting on the carbon and nitrogen fluxes through podzolic soil horizons

Effects of clear-cutting on the dissolved fluxes of organic C (DOC), organic N (DON), NO₃ ^– and NH₄ ⁺ through surface soil horizons were studied in a Norway spruce dominated mixed boreal forest in eastern Finland. Bulk deposition, total throughfall and soil water from below the organic (including understorey vegetation and, after clear-cutting, also logging residues), eluvial and illuvial horizons were sampled weekly from 1993 to 1999. Clear-cutting was carried out in September 1996. The removal of the tree canopy decreased the deposition of DOC and DON to the forest floor and increased that of NH₄ ⁺ and NO₃ ^– but did not affect the deposition of total N (DTN, <3 kg ha^–1 a^–1). The leaching of DOC and DON from the organic horizon increased over twofold after clear-cutting (fluxes were on an average 168 kg C and 3.3 kg N ha^–1 a^–1), but the increased outputs were effectively retained in the surface mineral soil horizons. Inorganic N deposition was mainly retained by the logging residues and organic horizon indicating microbial immobilization. Increased NO₃ ^– formation reflected as elevated concentrations in the percolate from below the mineral soil horizons were observed especially in the third year after clear-cutting. However, the changes were small and the increased leaching of DTN from below the illuvial horizon remained small (<0.4 kg ha^–1 a^–1) and mainly DON. Effects of clear-cutting on the transport of C and N to surface waters will probably be negligible.     

Effects of forest clear-cutting and soil disturbance on the biology of small forest brooks

As a part of the larger Nurmes research project, we studied the effects of clear-cutting and soil disturbance (ditching, ploughing, mounding) on the biology of small forest brooks. After these forestry activities, incoming light, temperature, and nutrient content of the water increased significantly. Mean algal biomass peaked during the first summer after clear-cutting. During the first year following soil disturbance, algal biomass initially decreased because of turbidity, but began to rise again as suspended solids in the water decreased in the summer months. Species composition changed, too; after clear-cutting, Cryptomonas and Chlamydomonas species increased their densities (48% of the algal biomass) and following soil disturbance, the species numbers and densities of Conjugatophyceae (52% of the algal biomass) were higher than before. Canonical correspondence analysis suggested that increased nutrient levels and acidity were the main factors behind the changes in the flora following clear-cutting. The most important effect of soil disturbance was the increased water temperature. Effects of forest clear-cutting on algal productivity in the brooks remain evident at least for three years and those of soil disturbance for an even longer period. Restricted clear-cutting, with a protective zone left uncut around the brooks, appears to reduce the effects.     

Resuspension in a shallow eutrophic lake

The frequency and the importance of wind-induced resuspension were studied in the shallow, eutrophic Lake Arresø, Denmark (41 km², mean depth 3 m). During storm events in autumn 1988 lake water samples were collected every 2–8 hours by an automatic sampler at a mid-lake station. The concentration of suspended solids and Tot-P was found to increase markedly. During storms up to 2 cm of the superficial sediment was resuspended, and the concentration of resuspended solids in the water column rose to 140 mg l^–1. The resuspended particles had a relatively high settling velocity and on average, a relatively short residence time in the water column of 7 hours.A model which describes the concentration of resuspended solids as a function of wind velocity and of settling velocity of the resuspended particles is presented. Using additional wind velocity data from a nearby meteorological station, the model has been used to calculate the frequency of resuspension events and concentration of resuspended solids for the period from May to November 1988.These calculations show that resuspension occurred about 50% of the time. Average flux of suspended solids from the sediment to the water was 300 g m^–2 d^–1 and during 50% of the time lake water concentration of suspended solids was more than 32 mg l^–1. A relationship between concentration of suspended solids and Secchi-depth is presented. Because of resuspension, Secchi-depth in Lake Arresø is reduced to 0.5 m.Resuspension also had a marked effect on Tot-P concentration in the lake water, and P input to the lake water being totally dominated by resuspension events.     

The role of rock weathering in the phosphorus budget of terrestrial watersheds

Residual soils (saprolites) developed on crystalline rocks appear to form by an essentially isovolumetric process (i.e. without dilation or compaction). Isovolumetric geochemical analysis of a suite of saprolite samples developed on a common parent rock can be used to estimate the relative rates of long-term losses of P and Si during weathering. Using the export of dissolved Si in rivers as a weathering index, one can then estimate the rate of P release due to chemical weathering by means of the P-Si loss ratio in saprolite. For three basins where data are available (Liberty Hill, SC; Amazon River, Brazil: Rio Negro, Brazil) estimated P weathering release rates are 163, 457, and 242 moles P km^–2 yr^–1 respectively. These compare to precipitation inputs of 684, 700 and 630 moles P km^–2 yr^–1 and total river exports of 256, 4490 and 820 moles P km^–2 yr^–1, respectively. The Rio Negro shows a near perfect balance between the input of P via precipitation and chemical weathering and the riverine output of dissolved and suspended P. This system, however, raised the unsolved problem of the source that supports the atmospheric P input.     

Zooplankton and environmental characteristics of Shiroro Lake at the extremes of its hydrological cycle

We studied the newly-created Shiroro lake, Nigeria, at the extremes of its hydrological cycle: high water level (HWL) and low water level (LWL). Temperatures reflected prevailing weather conditions; pH, dissolved oxygen, turbidity and suspended solids were highest during HWL, but transparency, conductivity, NO ₃ ^– -N, PO ₄ ^3– -P and Na⁺ were higher during LWL. A total of twenty-six species of pelagic zooplankton were identified: five species of cladocerans, eight species of copepods, and thirteen species of rotifers. The freshwater medusa (Limnocnida) and Daphnia longispina were absent during HWL but present at LWL, suggesting seasonality of the zooplankton community. Thermocyclops consimilis and T. emini are new records for Nigeria, bringing to nine the number of known Thermocyclops species in Nigeria.     

The impacts of re-introducing Mississippi River water on the hydrologic budget and nutrient inputs of a deltaic estuary

Most wetlands of the Mississippi deltaic plain are isolated from riverine input due to flood control levees along the Mississippi River. These levees have altered hydrology and ecology and are a primary cause of massive wetland loss in the delta. River water is being re-introduced into coastal basins as part of a large-scale ecological engineering effort to restore the delta. We quantified freshwater, nitrogen, and phosphorus inputs to the Breton Sound Estuary for three climatically different years (2000, 2001, and 2002). Water budgets included precipitation, potential evapotranspiration, the diversion, stormwater pumps, and groundwater. Precipitation contributed 48–57% of freshwater input, while the diversion accounted for 33–48%. Net groundwater input accounted for less than 0.05% of freshwater inputs. Inputs of ammonium (NH₄-N), nitrate (NO₃-N), total nitrogen (TN), and total phosphorus (TP) were determined for each of the water sources. Atmospheric deposition was the most important input of NH₄-N (57–62% or 1.44 × 10⁵–2.32 × 10⁵ kg yr⁻¹) followed by the diversion. The diversion was the greatest source of NO₃-N (67–83%, 7.78 × 10⁵–1.64 × 10⁶ kg yr⁻¹) and TN (60–71%). The diversion contributed 41–60% of TP input (1.17 × 10⁵–2.32 × 10⁵ kg yr⁻¹). Annual loading rates of NH₄-N and NO₃-N were 0.17–0.27 and 1.2–2.3 g N m⁻² yr⁻¹, respectively, for the total basin indicating strong retention of nitrogen in the basin. Nitrogen retention through denitrification and burial was estimated for the upper basin.     

Managing runoff,water quality and erosion in peatland forestry by peak runoff control

Retention of stormwater can in theory reduce peak flows, sediment and nutrient transport. This study presents results of peak runoff control (PRC) as a water protection method to decrease sediment and nutrient loads from drained peatland forestry in boreal conditions. Peak runoff rate and peak concentrations were reduced. The PRC method reduced suspended solids (SS) load (86%) by reducing flow velocities and improving settling conditions in the ditch network. The method had a considerable effect on SS-bound nutrients, reducing total nitrogen (N_tot) load by 65% and total phosphorus (P_tot) load by 67%. Reductions in velocity resulted in smaller particle size distributions in transported SS. No effect on groundwater elevation was observed and drainage conditions for forestry were maintained. The results clearly show that the PRC method can be used efficiently in peatland forestry as a water protection method to improve water quality.     

Influence of the pH and redox potential on phosphate activity in the Parana Medio system

The effect of redox potential and pH on the phosphate mobility in two sediments were investigated using both consolidated and suspended sediments from the area where the Parana Medio long reservoir (Atgentina) is to be built (Smirnov, 1984). In addition to direct chemical sediment analysis, extraction techniques were carried out with a stepwise NH₄Cl-NaOH-HCl shaking method, the latter supposedly separating the weakly bound, the Fe- and Al- bound and the Ca- bound phosphates in the sediments.Phosphate released into water depends upon redox potential and pH, which both were modified in an experimental setup. The source of the phosphate was the fraction of Fe and/or Al bound phosphate present both in the sediment and in the suspended solids.Abbreviations cm centimeter - km kilometer - gg gram - l liter - ¬m micrometer - °C grade centigrades - km² square kilometer - m.s^–1 meter per second - m³.s^–1 cubic meter per second - mg.1¹ miligram per liter     

Effects of forest clear-cutting on the sulphur, phosphorus and base cations fluxes through podzolic soil horizons

Clear-cutting considerably alters the flow of nutrients through the forest ecosystem. These changes are reflected in soil solution concentrations and fluxes. The effects of clear-cutting (stems only) on the fluxes of water soluble phosphorus (P), sulphur (S) and base cations (Ca, Mg and K) through a podzolic soil were studied in a Norway spruce dominated mixed boreal forest in eastern Finland. Bulk deposition, total throughfall (throughfall + stemflow) and soil percolate from below the organic (O), eluvial (E) and illuvial (B) horizons were collected for 4 years before and for 3 years after cutting. Annual deposition loads (kg ha^–1) to the forest floor were less after clear-cutting, averaging 1.7 S, 0.84 Ca, 0.14 Mg, 0.64 K and 0.10 P. Before cutting, the loads were 4.6 S, 2.7 Ca, 0.70 Mg, 6.2 K and 0.20 P. Annual fluxes of total S and sulphate (SO ₄ ^2– ) from below the O-horizon were also lower (33%) after clear-cutting, total S averaging 2.0 kg ha^–1, the flux from below the B-horizon also diminished after clear-cutting. The flux of total P (mainly inorganic) from below the O-horizon increased threefold (6.9 kg ha^–1; sum over the 3-year period) compared to period before cutting. The fluxes of base cations from below the O-horizon increased twofold. The flux of K⁺ from below the O- and E-horizons was most strongly correlated with that of phosphate (PO ₄ ^3– ) and those of Ca²⁺ and Mg²⁺ with the DOC flux. Increased fluxes of P and base cations to the mineral soil generated only slightly increased fluxes from below the B-horizon. The retention of base cations and P in the mineral soil indicates there was little change in leaching to ground and surface waters after clear-cutting.     

The influence of nitrogen concentration and ammonium/nitrate ratio on N-uptake,mineral composition and yield of citrus

In short-term water culture experiments with different ¹⁵N labeled ammonium or nitrate concentrations, citrus seedlings absorbed NH₄ ⁺ at a higher rate than NO₃ ^–. Maximum NO₃ ^– uptake by the whole plant occurred at 120 mg L^–1 NO₃ ^–-N, whereas NH₄ ⁺ absorption was saturated at 240 mg L^–1 NH₄ ⁺-N. ¹⁵NH₄ ⁺ accumulated in roots and to a lesser degree in both leaves and stems. However, ¹⁵NO₃ ^– was mostly partitioned between leaves and roots.Adding increasing amounts of unlabeled NH₄ ⁺ (15–60 mg L^–1 N) to nutrient solutions containing 120 mg L^–1 N as ¹⁵N labeled nitrate reduced ¹⁵NO₃ ^– uptake. Maximum inhibition of ¹⁵NO₃ ^– uptake was about 55% at 2.14 mM NH₄ ⁺ (30 mg L^–1 NH₄ ⁺-N) and it did not increase any further at higher NH₄ ⁺ proportions.In a long-term experiment, the effects of concentration and source of added N (NO₃ ^– or NH₄ ⁺) on nutrient concentrations in leaves from plants grown in sand were evaluated. Leaf concentration of N, P, Mg, Fe and Cu were increased by NH₄ ⁺ versus NO₃ ^– nutrition, whereas the reverse was true for Ca, K, Zn and Mn.The effects of different NO₃ ^–-N:NH₄ ⁺-N ratios (100:0, 75:25, 50:50, 25:75 and 0:100) at 120 mg L^–1 total N on leaf nutrient concentrations, fruit yield and fruit characteristics were investigated in another long-term experiment with plants grown in sand cultures. Nitrogen concentrations in leaves were highest when plants were provided with either NO₃ ^– or NH₄ ⁺ as a sole source of N. Lowest N concentration in leaves was found with a 75:25 NO₃ ^–-N/NH₄ ⁺-N ratio. With increasing proportions of NH₄ ⁺ in the N supply, leaf nutrients such as P, Mg, Fe and Cu increased, whereas Ca, K, Mn and Zn decreased. Yield in number of fruits per tree was increased significantly by supplying all N as NH₄ ⁺, although fruit weight was reduced. The number of fruits per tree was lowest with the 75:25 NO₃ ^–-N:NH₄ ⁺-N ratio, but in this treatment fruits reached their highest weight. Rind thickness, juice acidity, and colour index of fruits decreased with increasing NH₄ ⁺ in the N supply, whereas the % pulp and maturity index increased. Percent of juice in fruits and total soluble solids were only slightly affected by NO₃ ^–:NH₄ ⁺ ratio.     

Effects of food and silt on filtration,respiration and condition of the freshwater mussel Hyridella menziesi (Unionacea: Hyriidae): implications for bioaccumulation

The effect of exposure to different concentrations of food and suspended silt on filtration, respiration and condition were studied in the freshwater mussel Hyridella menziesi. Using a milk solids-based food and kaolin to simulate silt, mussels were maintained at different combinations of food and silt concentrations for 3 weeks. Between treatments mean filtration rates ranged from 0.97–1.66 l g^–1 h^–1, and respiration from 0.50–1.35 mg O₂ g^–1 h^–1. Silt (non-volatile suspended solids up to 35 mg l^–1) failed to have a significant effect on filtration rate or condition, but with increasing food levels (volatile suspended solids up to 35 mg l^–1) filtration rate was reduced, and condition was reduced at the lowest food concentration (<5 mg l^–1). Respiration showed a food × silt interaction between treatment blocks. When food was low respiration increased with increasing silt concentrations, and when silt was low (<5 mg l^–1) respiration increased with increasing food concentrations. The observed effects of food and silt on filtration, respiration and condition are discussed in terms of their potential for affecting contaminant bioaccumulation. In low-food situations (i.e., <5 mg l^–1), if mussels are pumping large volumes of water, contaminant uptake rates could be enhanced, whereas abundant food would result in lower pumping rates and lower uptake rates. Changes in metabolism with food concentration have implications for contaminant elimination, and changes in biochemical composition associated with changing condition could affect the tissue distribution and retention of contaminants.     

Effect of Fluoride on Nitrification of a Concentrated Industrial Waste

The potential for biological nitrification of an industrial waste containing 4,000 mg of ammonia N (NH₄⁺-N) and 10,000 mg of fluoride per liter was investigated. Ammonium sulfate and sodium fluoride were tested in various combinations of 100 to 2,000 mg of NH₄⁺-N per liter and 0 to 5,000 mg of F⁻ per liter in suspended-growth stirred-tank reactors containing enriched cultures of nitrifying bacteria from a municipal sewage treatment plant. The stirred-tank reactors were fed once per day at a constant hydraulic retention period and cell retention time of 10 days. Temperature was 23°C, and pH was 7.0 to 7.5. Clarified secondary effluent was used to make up feeds and to provide minor nutrients. Steady-state data, confirmed by mass balances, were obtained after five to six retention periods. In the absence of fluoride, nitrification efficiency was near 100% for up to 500 mg of NH₄⁺-N per liter. The influence of fluoride was studied at a low ammonia concentration (100 mg/liter) and exerted no significant effect on nitrification at concentrations of up to 200 mg/liter. Maximum effect of fluoride was reached at 800 mg of F⁻ per liter, and no greater inhibition was observed for up to 5,000 mg of F⁻ per liter. At the highest concentrations studied, ion pairing of ammonium and fluoride may exert a significant effect on kinetic coefficients. Kinetic analyses showed maximum specific substrate removal rates (q_max) of NH₄⁺-N to be about 2.3 mg of N per mg of volatile suspended solids per day in the absence of fluoride and 0.85 mg of N per mg of volatile suspended solids per day in the presence of fluoride. The form of inhibition due to the presence of fluoride was shown to be not competitive, conforming to a mixed inhibition model.     

Simultaneous nitrification and denitrification in a mixed methanotrophic culture

Simultaneous nitrification and denitrification using a mixed methanotrophic culture was investigated. When both NO₃ ^–-N (108 mg l^–1) and NH₃-N (59 mg l^–1) were added into batch reactors, nitrate removal was complete within 10 h at the rate of 47 mg NO₃ ^–-N g VSS^–1 day^–1 when dissolved oxygen (DO) concentration was maintained at 2 mg DO l^–1. Ammonia removal started simultaneously with nitrate removal at a slower rate of 14 NH₃-N g VSS^–1 day^–1. No significant accumulation of nitrite or nitrate during ammonia utilization suggested the occurrence of simultaneous nitrification and denitrification.     

Thermophilic H2 production from a cellulose-containing wastewater

Cellulose in wastewater was converted into H₂ by a mixed culture in batch experiments at 55°C with various wastewaters pH (5.5–8.5) and cellulose concentrations (10–40 g l^–1). At the optimal pH of 6.5, the maximum H₂ yield was 102 ml g^–1 cellulose and the maximum production rate was 287 ml d^–1 for each gram of volatile suspended solids (VSS). Analysis of 16S rDNA sequences showed that the cellulose-degrading mixed culture was composed of microbes closely affiliated to genus Thermoanaerobacterium.     

Studies in nitrification of municipal sewage in an upflow biofilter

The upflow aerated biofilter with polyurethane foam cubes as the supporting medium was used for the investigation of nitrification studies on municipal sewage (secondary treated as well as untreated domestic sewage). In case of secondary treated sewage effluent, a synthetic composition of NH₄ ⁺-N and COD of each 50?mg/l was studied for a HRT variation of 24, 12, 8 and 6 hours. The ammonium removal efficiencies were found to be in the range of 98 to 100% with the steady-state effluent concentrations of NH₄ ⁺-N and NO₂ ^?-N in the range of 1–4 mg/l and 0.1–0.2?mg/l respectively. In case of domestic sewage system, nitrification studies along with suspended solids removal study was carried-out on untreated sewage for a HRT variation of 24, 12 and 6 hours. The ammonium removal efficiencies of 100% were observed for all the three HRT values at very high COD/NH₄ ⁺-N ratio of 15. The suspended solids removal efficiencies of 95 to 98% were observed with the average effluent suspended solids concentration of 5.9 to 15.9?mg/l. The experiments were conducted in non-backwash conditions of the biofilter. The study has revealed the best use of the upflow biofilter system for nitrification applications and suspended solids removal.     

Biodegradability and toxicity of styrene in the anaerobic digestion process

Start-up and operation of an Upflow Anaerobic Sludge Blanket (UASB) reactor fed with an industrial effluent from a polymer synthesis plant containing 6 mg styrene l^–1 was unstable. In batch assays with 200 mg styrene l^–1, 74% of styrene was degraded at a rate of 7 ml methane g^–1 volatile suspended solids.day, without a lag phase. The toxicity limit (IC₅₀) of styrene was 1.4 mM for the acetoclastic activity, 0.45 and 1.6 mM for the methanogenic activity in the presence of 30 mM of propionate and ethanol respectively. Instability of UASB operation was attributed to other compounds such as acrylates or detergents present in the industrial effluent.