Chemical-mechanical characteristics of crushed oyster-shell

Enormous amount of oyster-shell waste has been illegally disposed at oyster farm sites along the southern coast of Korea. To seek for a possibility to recycle the waste as construction materials, chemical and mechanical characteristics of crushed oyster-shell were investigated. Chemical and microstructure analyses showed that oyster-shells are predominantly composed of calcium carbonate with rare impurities. Compressive strength tests for soil mortar specimens with varying blending ratio of cement, water, sand, and oyster-shell were compared with normal cement mortar. There was no significant reduction in the compressive strength up to 40% of dosages of oyster-shell instead of sand. The experimental results demonstrate that oyster-shells can be resources of pure calcareous materials and effective in replacement of sand, indicating promising reusable construction materials.     

Composition of a Spanish sewage sludge and effects on treated soil and olive trees

The effects of sewage sludge (SL) application on the soil and olive trees (Olea europaea L., cultivar: cornicabra) were studied. The plants were grown in 8.5L pots and subjected to the following treatments: 0, 3.66, 7.32, 14.65, 29.3, 58.6, and 117.2 g SL kg(-1) soil that corresponded, respectively, to 0, 4, 8, 16, 32, 64 and 128 M g ha(-1) dry weight of sewage sludge. The application of SL at the rates 64 and 128 M g ha(-1) produced leaf tip burning and leaf drop after 120 days, although cumulative metal pollutant loading rates was below USEPA and European regulations. This toxicity symptom could be caused by the high sodium levels in the leaves (over 0.19%), which can damage olive tree development. The Na contents of leaves were well correlated with soil Na content (r2: 0.91). In general, SL rates significantly increased the level of Cr, Ni, Cu, Zn, Cd and Pb in soil and plants, but these concentrations were in the normal ranges, except for the Zn concentration, which was over the critical soil content for the rates of 32, 64, 128 Mg ha(-1) but not in the leaves. Results suggested that regulations about the utilization of sewage sludge on agricultural land should consider the limit values for salt, and not only metals, that may be added to soil, in order to minimize the risk of negative effects to plant health.     

内酯型槐糖脂修复石油污染土壤的影响因素

采用内酯型槐糖脂(SL50)修复石油污染土壤。通过单因子实验与正交实验,考察了槐糖脂溶液质量浓度、振荡时间、反应体系初始pH、NaCl加入量以及固液比(土壤质量与表面活性剂溶液体积之比)对污染土壤石油烃洗脱率的影响。单因子模型回归分析结果表明,参数变量均符合二次拟合模型,槐糖脂溶液质量浓度、反应体系初始pH以及NaCl加入量的二次模型拟合效果较好。正交实验结果表明,槐糖脂溶液质量浓度和反应体系初始pH是该实验的敏感性因子,最优洗脱条件为槐糖脂溶液质量浓度40 mg/L、反应体系初始pH 9、NaCl加入量6%(w)。     

Crop residues as soil amendments and feedstock for bioethanol production

Traditional solid fuels account for more than 90% of the energy supply for 3 billion people in developing countries. However, liquid biofuels (e.g., ethanol) are perceived as an important alternative to fossil fuel. Global crop residue production is estimated at about 4 billion Mg for all crops and 3 billion Mg per annum for lignocellulosic residues of cereals. One Mg of corn stover can produce 280L of ethanol, compared with 400L from 1Mg of corn grains; 1Mg of biomass is also equivalent to 18.5GJ of energy. Thus, 3 billion Mg of residues are equivalent to 840 billion L of ethanol or 56x10(9)GJ of energy. However, removal of crop residues exacerbates soil degradation, increases net emission of CO2, and aggravates food insecurity. Increasing the SOC pool by 1 Mg C ha(-1)yr(-1) through residue retention on soil can increase world food grain production by 24-40 million Mg yr(-1), and root/tuber production by 6-11 million Mg yr(-1). Thus, identifying alternate sources of biofuel feedstock (e.g., biofuel plantations, animal waste, municipal sold waste) is a high priority. Establishing biofuel plantations on agriculturally marginal or degraded lands can off-set 3.5-4 Pg Cyr(-1).     

Modification of soil humic matter after 4 years of compost application

Two soil plots, 1 ha each, were amended yearly for 4 years, respectively, with 35.8 and 71.6 Mg ha(-1) yr(-1) of mature compost (CM) obtained from food and vegetable residues. The compost, amended soils, and a control soil plot after 4 years (S4), were analyzed for humin (HUC), humic acid (HAC), fulvic acid (FAC), and non-humic carbon (NHC) content. Compared to S4, the amended soil contained more humified C (HAC, FAC and HUC) and less NHC. Further evidence of the effect of compost on soil organic matter was obtained by the analysis of the humic acid (HA) fractions isolated from both the compost and the soils. These were characterized by elemental analyses and Diffuse Reflectance Infrared Fourier Transformed spectroscopy. The HAs isolated from CM and from S4 were significantly different. The HAs isolated from the amended plots were more similar to HA isolated from CM than to HA isolated from S4. The experimental data of this work indicate that the compost application may affect significantly the soil organic matter composition, and that the approach used in this work allows one to trace the fate of compost organic matter in soil.     

Effects of Acidification and its Mitigation with Lime and Wood Ash on Forest Soil Processes in Southern Sweden. A Joint Multidisciplinary Study

A joint multidisciplinary investigation was undertaken to studythe effects of lime and wood ash applications on two Norway spruce forest Spodosolic soils. The two sites, typical for southern Sweden, were treated in 1994 with either 3.25 t ha^-1 dolomite or 4.28 t ha^-1 wood ash (Horröd site) or in 1984 with either 3.45 or 8.75 t ha^-1 dolomite (Hasslöv site). Both sites show signs of acidification by atmospheric anthropogenic deposition and possessed low soil pH(4.3) and high concentrations of inorganic Al (35 M) in theupper illuvial soil solution. The prevailing soil conditions indicated perturbed soil processes. Following treatment with lime or wood ash, the soil conditions were dramatically altered. Cation exchange capacity (CEC) and base saturation (BS) was considerable increased after addition. Four years after application most of the added Ca and Mg was still present in the mor layer. Fifteen years after application,Mg in particular, became integrated deeper in the soil profile with a greater proportion lost by leaching incomparison to Ca. The concentrations of these ions were greatestin the mor layer soil solutions and Mg had higher mobility givinghigher concentrations also deeper in the profile. Four years after treatment, the application of wood ash and limeresulted in lower pH values and higher inorganic Al in mineral subsoil solutions compared to the untreated soil. We hypothesize that this was probably due to an increased flow of hydrogen ionsfrom the upper soil as a result of displacement by Ca and Mg ionsin the enlarged exchangeable pool. In contrast, fifteen years after lime and wood ash application, the mineral subsoil horizonspossessed a higher pH and lower soil solution Al content than theuntreated plots.Liming promoted soil microbial activity increasing soil respiration 10 to 36%. This is in the same range as net carbon exchange for forests in northern Sweden and could potentially have a climatological impact. The turnover of low molecularweight organic acids (LMWOA) by the soil microbial biomass werecalculated to contribute 6 to 20% to this CO₂ evolution.At Horröd, citrate and fumarate were the predominant LMWOAs with lowest concentrations found in the treated areas. In contrast, at the Hasslöv site, propionate and malonate were the most abundant LMWOAs. Higher microbial activity in the upper soil horizons was also theprobable cause of the considerably higher DOC concentrations observed in the soil solution of ash and lime treated areas. Thelime-induced increase in DOC levels at Hasslöv could be attributed to increases in the 3–10 kDa hydrophobic size fraction. Liming also promoted nitrification with high liming doses leading to extreme concentrations of NO₃ ^- (1 mM) in soil solution.At Hasslöv the community of mycorrhizal fungi was dramatically changed by the addition of lime, with only four of 24 species recorded being common to both control and treated areas.Many of the observed effects of lime and ash treatment can be viewed as negative in terms of forest sustainability. After fouryears of treatment, there was a decrease in the pH of the soil solution and higher concentrations of inorganic Al and DOC. Increased organic matter turnover, nitrification and NO₃ ^-leakage were found at Hasslöv. Considering that the weathering rate and the mineral nutrient uptake by trees is mostprobably governed by mycorrhizal hyphae etchingmineral grains in the soil, it is important to maintain this ability of the mycorrhizal fungi. The lime and ash-induced changed mycorrhizal community structure may significantly affect this capability. In light of this investigation and others, as reviewed by Lundström et al. (2003), the implications ofliming on forest health are multifaceted with complex relationships occurring over both space and time.     

Oyster shell as substitute for aggregate in mortar.

Enormous amounts of oyster shell waste have been illegally disposed of at oyster farm sites along the southern coast of Korea. In this study to evaluate the possibility of recycling this waste for use as a construction material, the mechanical characteristics of pulverized oyster shell were investigated in terms of its potential utilization as a substitute for the aggregates used in mortar. The unconfined compressive strengths of various soil mortar specimens, with varying blending ratios of cement, water and oyster shell, were evaluated by performing unconfined compression tests, and the results were compared with the strengths of normal cement mortar made with sand. In addition, the effect of organic chemicals on the hardening of concrete was evaluated by preparing ethyl-benzene-mixed mortar specimens. The long-term strength improvement resulting from the addition of fly ash was also examined by performing unconfined compression tests on specimens with fly-ash content. There was no significant reduction in the compressive strength of the mortars containing small oyster shell particles instead of sand. From these test data, the possible application of oyster shells in construction materials could be verified, and the change in the strength parameters according to the presence of organic compounds was also evaluated.     

Simultaneous treatment of PVC and oyster-shell wastes by mechanochemical means

This work presents a new process for dechlorinating poly-vinyl chloride (PVC) by the use of oyster-shell waste. The process consists of milling of PVC waste with oyster-shell waste, followed by washing the milled sample with water. The milling of PVC and oyster-shell mixture results in size reduction and rupture in bonds, leading to mechanically induced reactions between the two to form CaCl2 and hydrocarbon with C=C bonds. Washing the milled mixtures with water at room temperature allows complete removal of chlorine from the milled sample. More than 95% of chlorine in PVC was removed when 2h grinding is conducted for the mixture. The present process could offer a potential route to the handling and disposal of oyster-shell and PVC wastes.     

Pools and Fluxes of Cations,Anions and Doc in Two Forest Soils Treated With Lime and Ash

The effect of liming and ash treatment on pools, fluxes and concentrations of major solutes was investigated at two forestedsites (Norway spruce) in S. Sweden. One site was treated 15 yrprior to sampling (Hasslöv-Hs; dolomite: 3.45 and 8.75 t ha^-1) and the other 4 yr before (Horröd-Hd; dolomite: 3.25 t ha^-1; wood ash: 4.28 t ha^-1). Effects of limingwere most pronounced in the O horizon solutions where higher pH,elevated Ca (120–700 M) and Mg (50–600 M) were observed as compared to control plots. The impact on the mineralsoil was more moderate. Soil solution concentrations were combined with modelled hydrological flow to calculate mass flows,which largely followed the trends of the solution composition. Liming also resulted in large increases of both exchangeable Caand Mg as well as effective cation exchange capacity (CEC_E;2–5 times the controls). The base saturation (BS%) was raised to 60–100% in the O horizon while in the mineral soil elevated values were only seen at the Hs site (20–60%; down to 10–15 cm depth for 8.75 t ha^-1). Ash treatment did notaffect either the soil solution nor the exchangeable pool to thesame extent as lime. In general, the impact at the Hd site was less pronounced especially in the mineral soil, which might be due to shorter treatment time (4 vs. 15 yr) and also differentthickness of the O horizon. Budget calculations for Ca and Mg originating from the lime showed that a major part of the Ca (40–100%) was retained in the top 30 cm of the soil, of which30–95% was present in the O horizon. The mobility of Mg wasgreater and it was estimated that a significant part had been leached from the profile (30 and 50 cm depth) after 15 yr. Increased mass flows of NO₃ ^- due to nitrification resulting from liming at the Hs site were calculated in the range120–350 mmol m^-2 yr^-1 (or 1.2–3.5 kmol ha^-1 yr^-1). There was significant leaching of Al (25–60 mmol m^-2 yr^-1), of which about 70% was inorganic, in thelower B horizon at both sites with no influence of liming.     

Compost impacts on dissolved organic carbon and available nitrogen and phosphorus in turfgrass soil

Compost application to turfgrass soils may increase dissolved organic C (DOC) levels which affects nutrient dynamics in soil. The objectives of this study were to investigate the influence of compost source and application rate on soil organic C (SOC), DOC, NO(3), and available P during 29 months after a one-time application to St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] turf. Compost sources had variable composition, yet resulted in few differences in SOC, DOC, and NO(3) after applied to soil. Available NO(3) rapidly decreased after compost application and was unaffected by compost source and application rate. Available P increased after compost application and exhibited cyclical seasonal patterns related to DOC. Compost application decreased soil pH relative to unamended soil, but pH increased during the course of the study due to irrigation with sodic water. Increasing the compost application rate increased SOC by 3 months, and levels remained fairly stable to 29 months. In contrast, DOC continued to increase from 3 to 29 months after application, suggesting that compost mineralization and growth of St. Augustinegrass contributed to seasonal dynamics. Dissolved organic C was 75%, 78%, and 101% greater 29 months after application of 0, 80, and 160 Mg compostha(-1), respectively, than before application. Impacts of composts on soil properties indicated that most significant effects occurred within a few months of application. Seasonal variability of SOC, DOC, and available P was likely related to St. Augustinegrass growth stages as well as precipitation, as declines occurred after precipitation events.     

Biodegradation of Low Molecular Weight Organic Acids in a Limed Forest Soil

The effect of liming (3.45 and 8.75 t ha^-1 dolomite; 16 yr after application) on the biodegradation of three low molecular weight organic acids (citrate, oxalate and propionate) in forest soils was investigated. The concentration of organic acids in the soil solution followed the series propionate > citrate > oxalate with liming having no significant impact on soil solution concentrations (mean organic acid concentration = 8.7 ± 2.3 M). Organic acid mineralization by the soil microbial community was rapid in surface organic horizons (mean half-life for citrate = 2–6 h), with biodegradation rate gradually declining with soil depth. Concentration-dependent biodegradation studies (0 to 350 M) showed that the mineralization kinetics generally conformed well to a single Michaelis–Menten equation with V_max values following the series oxalate > citrate > propionate (mean = 9.8 ± 1.0 nmol g^-1 h^-1) and K_M values following the series oxalate = citrate > propionate (mean 168 ± 25 M). The V_max values declined with soil depth, which was consistent with a general reduction in microbial activity down the soil profile. Liming induced a significant increase in V_max for citrate with no change for propionate and reduction in V_max for oxalate. The latter was probably due to adsorption and precipitation of Ca-oxalate making it unavailable for microbial uptake. The higher adsorption/precipitation capacity for oxalate in the limed soils was confirmed by adsorption isotherms. Generally, liming increased soil microbial activity by approximately 10 to 35% with calculations based on soil solution concentrations indicating that organic acid mineralization constituted approximately 3 to 15% of the total soil respiration.     

Direct and Indirect Effects of Soil Pollution by Lignite Mining

Lignite mining and processing has caused a pronounced impact both directly and indirectly on soils and ecosystems across large areas of the former GDR. We studied soils of pine forest ecosystems at sites affected by severe alkaline dust and sulphur deposition, stemming from lignite fired power plant emission, and at dumped sites from lignite mining. In this paper we summarize our main results and evaluate the long-term impact of lignite mining and combustion on the environment. The pine ecosystems on naturally developed soils show a clear effect of deposition history along a former deposition gradient with distinct changes in chemical properties of organic surface layers and mineral soil as well as in element turnover and cycling rates. Afforested sites on mining dumps are directly affected by the composition of the dumped substrates. Over a large area (800 km²) these substrates are dominated by Tertiary sediments with varying amounts of lignitic particles and pyrite that result in phytotoxic site conditions (pH < 3, high salt and metal contents). High amelioration doses of liming material (up to 200 t ha⁻¹) were applied for restoration purposes. We studied the development of these sites over a period of 60 years using a false-time series approach. Beside the extreme soil conditions, element budgets of these sites are characterized by very high element release rates over decades caused by pyrite oxidation and primary mineral weathering.     

Recovery of Acidified Streams in Forests Treated by Total Catchment Liming

Reduced emissions of acidifying pollutants have changed the acidification process, and as a result, forest soils and surface waters are slowly recovering in Sweden. However, model calculations show that some areas may never recover completely unless further measures, such as liming, are undertaken. Liming of surface waters (lakes, rivers and wetlands) has been successfully practised in Sweden since the 1970s, but repeated treatments are necessary. A full recovery of acidified lakes and streams without frequent liming is however not possible until soil acidification is reversed in the most strongly affected areas. In this study, the recovery of acidified streams was examined using ‘the total catchment approach’ i.e. treatment of both recharge and discharge areas. The aim was to compare the quantitative effect of different treatments on run off chemistry and the recovery of brown trout. Catchments in southwest Sweden were treated with a combination of 2 tons of wood ash and 4, 6 or 12 tons of crushed limestone per hectare in 1998/1999. Treatment of both recharge and discharge areas resulted in fast and significant changes in stream water quality, e.g. increased concentrations of calcium, higher pH and ANC and a decreased concentration of inorganic aluminium. The initial changes were dependent on the distribution of the applied lime between discharge and recharge areas rather than the average dose on the total catchment. Treatment of recharge areas only, resulted in smaller but still significant effects on calcium, pH and ANC in stream water. Furthermore, there was an initial leaching of nitrate but it was only minor compared with the elevated leaching that occurs after a clear-cut. As a result of the treatments, brown trout is now successfully reproducing. Olle Westling (deceased).     

Effect of compost application rate on carbon degradation and retention in soils

We investigated the effect of a single compost application at two rates (50 and 85Mgha(-1)) on carbon (C) degradation and retention in an agricultural soil cropped with maize after 150d. We used both C mass balance and soil respiration data to trace the fate of compost C. Our results indicated that compost C accumulated in the soil after 150d was 4.24Mgha(-1) and 6.82Mg C ha(-1) for 50 and 85Mg ha(-1) compost rate, respectively. Compost C was sequestered at the rate of 623 and 617g C kg(-1) compost TOC for 50 and 85Mgha(-1) compost dose, respectively. These results point to a linear response between dose of application and both C degradation and retention. The amount of C sequestered was similar to the total recalcitrant C content of compost, which was 586g C kg(-1) compost TOC, indicating that, probably, during the short experiment, the labile C pool of compost (414g C kg(-1) of compost TOC) was completely degraded. Soil respiration measured at different times during the crop growth cycle was stable for soils amended with compost (CO2 flux of 0.96+/-0.11g CO2 m(-2) h(-1) and 1.07+/-0.10g CO2 m(-2) h(-1), respectively, for 50 and 85Mgha(-1)), whereas it increased in the control. The CO2 flux due to compost degradation only, though not statistically significant, was always greatest for the highest compost doses applied (0.22+/-0.40g CO2 m(-2) h(-1) and 0.33+/-0.25g CO2 m(-2) h(-1) for the 50 and 85Mgha(-1) compost dose, respectively). This seems to confirm the highest C degradation for the 85Mgha(-1) compost dose as a consequence of the presence of more labile C. Unlike other studies, the results show a slight increase in the fraction of carbon retained with the increase in compost application rate. This could be due to the highly stable state of the compost prior to application, although it could also be due to sampling uncertainty. Further investigations are needed to better explain how the compost application rate affects carbon sequestration, and how characterization into labile and recalcitrant C can predict the amount of C sequestered in the soil.     

Dynamics of Cd, Cu and Pb added to soil through different kinds of sewage sludge

A greenhouse experiment was set up to study the distribution of Cd, Cu and Pb in three typical soils of the Pampas Region amended with sewage sludge. A sequential extraction procedure was used to obtain four operationally defined geochemical species: exchangeable, bound to organic matter, bound to carbonates, and residual. Two kinds of sewage sludge were used: pure sewage sludge and sewage sludge containing 30% DM of its own incinerated ash, at rates equivalent to a field application of 150 t DM ha(-1). Pots were maintained at 80% of field capacity through daily irrigation with distilled water. Soil samples were obtained on days 1, 60, 270 and 360, and then air-dried and passed through a 2 mm sieve for analysis. Results showed that sludge application increased the less available forms of Cd, Cu and Pb. The inorganic forms became the most prevalent forms for Cu and Pb, whereas Cd was only found in the residual fraction. The concentrations of OM-Cu and INOR-Cu in the amended soil samples were closely correlated with soil pH, whereas the chemical behavior of Cd and Pb did not depend on soil physico-chemical characteristics.     

电动力学作用下多溴联苯醚在土壤中的迁移特性

以4，4′-二溴联苯醚(BDE-15)为研究对象，探讨了电极电压、初始土壤pH、β-环糊精加入量、NaCl加入量等工艺条件对多溴联苯醚在土壤中迁移效果的影响。实验结果表明:在电极电压为5~15V范围内，随着电极电压的升高，土壤中BDE-15的迁移效果增强;初始土壤为酸性时、加入β-环糊精或NaCl后，土壤中BDE-15的迁移效果均增强。本实验选择的最佳工作条件为:电极电压15V，初始土壤pH3，β-环糊精的加入量3g，NaCl加入量5g。     

Chemical sequential extraction of heavy metals and sulphur in bottom ash and in fly ash from a pulp and paper mill complex

A five-stage sequential extraction procedure was used to determine the distribution of 11 metals (Cd, Cr, Cu, Mo, Pb, Zn, As, Co, V, Ni, Ba), and sulphur (S) in bottom ash and in fly ash from a fluidized bed co-combustion (i.e. wood and peat) boiler of Stora Enso Oyj Oulu Mill at Oulu, Northern Finland, into the following fractions: (1) water-soluble fraction (H2O); (2) exchangeable fraction (CH3COOH); (3) easily reduced fraction (NH2OH-HCl); (4) oxidizable fraction (H2O2 + CH3COONH4); and (5) residual fraction (HF + HNO3 + HCl). Although metals were extractable in all fractions, the highest concentrations of most of the metals occurred in the residual fraction. From the environmental point of view, this fraction is the non-mobile fraction and is potentially the least harmful. The Ca concentrations of 29.3 g kg(-1) (dry weight) in bottom ash and of 68.5 g kg(-1) (dry weight) in fly ash were correspondingly approximately 18 and 43 times higher than the average value of 1.6 g kg(-1) (dry weight) in arable land in Central Finland. The ashes were strongly alkaline pH (approximately 12) and had a liming effects of 9.3% (bottom ash) and 13% (fly ash) expressed as Ca equivalents (dry weight). The elevated Ca concentrations indicate that the ashes are potential agents for soil remediation and for improving soil fertility. The pH and liming effect values indicate that the ashes also have a pH buffering capacity. From the environmental point of view, it is notable that the heavy metal concentrations in both types of ash were lower than the Finnish criteria for ash utilization.     

Electrokinetic remediation of heavy metal-contaminated soils under reducing environments

This paper describes the migration of hexavalent chromium, Cr(VI), nickel, Ni(II), and cadmium, Cd(II), in clayey soils that contain different reducing agents under an induced electric potential. Bench-scale electrokinetic experiments were conducted using two different clays, kaolin and glacial till, both with and without a reducing agent. The reducing agent used was either humic acid, ferrous iron, or sulfide, in a concentration of 1000 mg/kg. These soils were then spiked with Cr(VI), Ni(II), and Cd(II) in concentrations of 1000, 500 and 250 mg/kg, respectively, and tested under an induced electric potential of 1 VDC/cm for a duration of over 200 h. The reduction of chromium from Cr(VI) to Cr(III) occurred prior to electrokinetic treatment. The extent of this Cr(VI) reduction was found to be dependent on the type and amount of reducing agents present in the soil. The maximum reduction occurred in the presence of sulfides, while the minimum reduction occurred in the presence of humic acid. The concentration profiles in both soils following electrokinetic treatment showed that Cr(VI) migration was retarded significantly in the presence of sulfides due both to the reduction of Cr(VI) to Cr(III) as well as an increase in soil pH. This low migration of chromium is attributed to: (1) migration of Cr(VI) and the reduced Cr(III) fraction in opposite directions, (2) low Cr(III) migration due to adsorption and precipitation in high pH regions near the cathode in kaolin and throughout the glacial till, and (3) low Cr(VI) migration due to adsorption in low pH regions near the anode in both soils. Ni(II) and Cd(II) migrated towards the cathode in kaolin; however, the migration was significantly retarded in the presence of sulfides due to increased pH through most of the soil. Initial high pH conditions within the glacial till resulted in Ni(II) and Cd(II) precipitation, so the effects of reducing agenets were inconsequential. Overall, this study demonstrated that the reducing agents, particularly sulfides, in soils may affect redox chemistry and soil pH, ultimately affecting the electrokinetic remediation process.     

Autotrophic Biological Denitrification for Complete Removal of Nitrogen from Septic System Wastewater

The overall objective of this research was to develop a reliable, robust, and maintenance-free passive system for biological denitrification in on-site wastewater treatment systems. The process relies on sulfur oxidizing denitrifying bacteria in upflow packed bioreactors. Since this process consumes alkalinity, it is necessary to add a solid-phase buffer that can scavenge the H⁺ as it is generated by the biologically-mediated reaction and arrest the drop in the pH value. This study investigated the use of limestone, marble chips and crushed oyster shell as solid-phase buffers that provide alkalinity. Two bench-scale upflow column reactors and two field-scale bioreactors were constructed and packed with sulfur pellets and an alkalinity source. The pilot scale bioreactors (∼200 L each) were installed at the Massachusetts Alternative Septic System Test Center (MASSTC) in Sandwich, MA. The pilot-scale bioreactors performed better when oyster shell was used as the solid-phase buffer vis-à-vis marble chips. In both (pilot-scale and laboratory-scale) systems, denitrification rates were high with the effluent NO₃ ⁻ —N concentration consistently below 8 mg/L.     

Long-Term Maintenance of Rapid Atrazine Degradation in Soils Inoculated with Atrazine Degraders

Two different microbial communities able to degrade atrazine (atz) were inoculated in four different soils. The most critical factor affecting the success of inoculation was the soil pH and its organic matter (OM) content. In two alkaline soils (pH > 7), some inoculations led immediately to a strong increase of the biodegradation rate. In a third slightly acidic soil (pH = 6.1), only one inoculum could enhance atz degradation. In a soil amended with organic matter and straw (pH = 5.7, OM = 16.5%), inoculation had only little effect on atz dissipation on the short as well as on the long-term. Nine months after the microflora inoculations, atz was added again and rapid biodegradation in all alkaline inoculated soils was recorded, indicating the long-term efficiency of inoculation. In these soils, the number of atz degraders was estimated at between 6.5 × 10³ and 1.5 × 10⁶ (g of soil)^-1, using the most probable number (MPN) method. Furthermore, the presence of the atz degraders was confirmed by the detection of the gene atzA in these soils. Denaturing gradient gel electrophoresis (DGGE) analysis of the 16S rDNA genes indicated that the inoculated bacterial communities had little effect on the patterns of the indigenous soil microflora.