Impact of COVID-19 restrictions on hourly levels of PM10, PM2.5 and black carbon at an industrial suburban site in northern Spain

Due to the COVID-19 pandemic, lockdown restrictions were established around the world. Many studies have assessed whether these restrictions affected atmospheric pollution. Comparison between them is difficult as the periods of time considered are generally not the same and thus, different conclusions may be reached. Besides, most of them consider mean daily pollutant concentration, despite differences being observed according to the time of day. In this study, the hourly levels of PM10, PM2.5 and black carbon (BC) in an industrial suburban area in the north of Spain were analysed from May 2019 to June 2020 and compared with those from the literature, using the same period in each case. In general, the highest concentrations were reached when the wind direction came from the southwest (where a steelworks, a coal-fired power plant and other industries are located) and during the night-time, both before and during the lockdown. The highest concentrations of PM10, PM2.5 and BC were observed from December to February (on average: 45, 17 and 1.3 μg m^-3, respectively). The decrease/increase in those pollutants levels during the lockdown were found to be highly dependent on the period considered. Indeed, PM10 can be found to decrease by up to 39% or increase by 12%; PM2.5 can decrease by 21% or increase by up to 36%; and BC, although it generally decreases (by up to 42%), can increase by 7.4%.

Impact of COVID-19 restrictions on the dry deposition fraction of settleable particulate matter at three industrial urban/suburban locations in northern Spain

Ninety 24-h samples of the dry deposition fraction of settleable particulate matter (DSPM) were collected at one suburban industrial site ('EMA') and two urban industrial sites ('Lauredal' and 'Laboratory') in the western area of Gijón (North of Spain) from December 2019 to June 2020. The levels registered point to an environmental issue that should receive close attention from environmental authorities. Before lockdown restrictions due to COVID-19 were established, all samples collected at the EMA site exceeded 300 mg·m^-2·d^-1 (the Spanish limit value until 2002). Large amounts of DSPM were also registered at the Lauredal and Laboratory sites, maximum levels reaching 1039.2 and 672.7 mg·m^-2·d^-1, respectively. Seven metals were analysed in DSPM samples: Al, Ca, Fe, K, Mg, Mn and Na. Fe reached the highest values: 2473.4, 463.4 and 293.3 mg·m^-2·d^-1 (EMA, Lauredal and Laboratory sites, respectively). This study quantifies the reductions in the DSPM levels registered (on average, 97.2, 73.5 and 90.5% at the EMA, Lauredal and Laboratory sites, respectively) during the lockdown, which involved the restriction of population mobility and industrial activity. The influence of wind speed and its direction were also assessed to better understand the role of these restrictions in the observed reductions. The concentrations of all the metals in the DSPM were reduced by more than 75%, on average, except for K at the Laboratory and Lauredal sites. These decreases were much higher than those found by other authors for smaller fractions of the atmospheric particulate matter (PM10, PM2.5). The findings of the present study highlight the importance of DSPM in highly industrialized urban/suburban locations and indicate the direction that legal measures might take, given the influence of anthropogenic emissions.

Removal of fluoride from coke wastewater by aluminum doped chelating ion-exchange resins: a tertiary treatment

Coke wastewater is one of the most problematic industrial wastewaters, due to its large volume and complex pollutant load. In this study, ion exchange technology was investigated with the objective of reducing the fluoride content of the effluent from a coke wastewater treatment plant (26.7 mg F^-/L). Two Al-doped exchange resins with chelating aminomethyl-phosphonic acid and iminodiacetic groups were assessed: Al-doped TP260 and TP207 resins, respectively. The effect of resin dosage, varying from 5 to 25 g/L, was evaluated. F^- removal was within the range 57.8-89.3% and 72.0-92.1% for Al-doped TP260 and TP207, respectively. A kinetic study based on a generalized integrated Langmuir kinetic equation fitted the experimental data (R² > 0.98). The parameters of the said kinetics met the optimal conditions for the ion exchange process, which seemed to be more favorable with Al-doped TP260 resin than with Al-doped TP207 resin, using the same resin dosage. Furthermore, the experimental data were well described (R² > 0.98) by Langmuir and Freundlich isotherm models, in agreement with the findings of the kinetic study: the maximum sorption capacity was obtained for the Al-doped TP260 resin.

Settleable matter in a highly industrialized area: Chemistry and health risk assessment

Settleable particulate matter (SPM) was collected at two sampling points within an urban area highly affected by nearby industrial activities. Total deposition values up to 386 mg ·m^-2·d^-1 were registered, the majority of samples exceeding the limit value established in the legislation in force in Spain until 2002 (300 mg·m^-2·d^-1). Dry deposition values showed high variability (8.6-830.3 mg·m^-2·d^-1). Forty-one metals and metalloids were analysed in the dry fraction of SPM, the main being Fe and Ca (maximums: 304.4 and 68.6 mg·m^-2·d^-1, respectively), followed by Al, Mg, Na, K, Mn, Ti, P and Zn. Trace elements like As and Pb reached up to 7.3 and 76.3 μg· m^-2·d^-1, respectively. Strong correlations (r > 0.90, p-value < 0.05) between Fe and other elements (Ca, Mn and Pb) were found at both sampling sites. Scanning electron microscopy confirmed the presence of these particles rich in Fe and Ca, in addition to other components, whose morphologies pointed out to anthropogenic sources. These results combined with meteorology data suggest a common industrial source contributing to the levels of these metals. Furthermore, a human health risk study was carried out to assess the potential carcinogenic and non-carcinogenic risks of exposure to thirteen elements in these particles (Al, As, Cd, Co, Cu, Mn, Mo, Ni, Pb, Sb, Sr, V and Zn). The highest levels of risk seemed to be associated with the presence of As, Pb and Sb.

Impact of organic loading rate and reactor design on thermophilic anaerobic digestion of mixed supermarket waste

A mixture of supermarket food waste from bakery, butchery, cooked meats and cheese, fishmonger, fruit, and vegetable sections was subjected to anaerobic digestion under thermophilic conditions (55 °C). Lab-scale induced bed reactors (IBR) and completely stirred tank reactors (CSTR) were operated at different organic loading rates (OLR), i.e., 3.0, 3.6 and 4.6 kg volatile solids (VS) per m³ of reactor and day. Regardless of the type of reactor, an OLR of 3.6 kg VS/m³·day was found to be the optimum, achieving up to 48.1% more methane production per kg of treated waste than for the other OLRs tested. In general, there were no statistically significant differences (p-value < 0.05) between IBR and CSTR performance at the same OLR tested. However, for the optimum OLR, the IBR achieved a mean methane production of 1.5 L CH₄/L_reactor·day (426.7 L CH₄/kg VS) and the highest VS removal (89.0%, on average). This reactor obtained 22.1% more CH₄ yield than the analogous CSTR and the highest methane content in the biogas (66.9% CH₄). Finally, the process was successfully tested under large-scale conditions (1.25 m³ IBR pilot-plant). The CH₄ production and the biodegradation yield were in line with those obtained in the lab-scale IBR.

Anthropogenic and meteorological influences on PM10 metal/semi-metal concentrations: Implications for human health

There is growing interest in investigating the human health risk associated with metals in airborne particulate matter. The objective of this paper is the health risk assessment of Al, Be, Sb, Sn, Ti and Tl in PM₁₀ under different advections of air masses. These metals/semi-metal were studied in samples collected in an area influenced by industrial activities in northern Spain with the aim of analysing the variations in PM₁₀ metal/semi-metal. Elemental concentrations were assessed over a period of one year in terms of air mass origin by means of back trajectories (HYSPLIT), the conditional probability function, polar plots, PM concentration roses, aerosol maps (NAAPs) and receptor modelling. The mean concentrations of Al, Be, Sb, Sn, Ti and Tl were 254, 0.02, 1.30, 1.15, 15.3 and 0.20  ng/m³, respectively, and were within the usual range for suburban stations in Europe. The highest levels were recorded during conditions of regional air mass origin, highlighting the importance of sources not far from the station. Under these circumstances, the renovation of air masses was not produced. The main sources of metals were anthropogenic, mostly related to the use of coal and coke production. In general, the cancer and non-cancer risk values obtained in this study fell within accepted precautionary criteria in all trajectory groups. However, in order to improve air quality and reduce risks to human health, the impact resulting from the joint inhalation of Al, Be, Sb, Sn, Ti and Tl should not be ignored when air masses are fundamentally of regional origin.

Inverted phase fermentation as a pretreatment for anaerobic digestion of cattle manure and sewage sludge

The aim of this research study was to analyse the effect of applying inverted phase fermentation (IPF) prior to the anaerobic digestion of cattle manure and sewage sludge. IPF promotes the endogenous bacteria present in waste and hence enzymatic hydrolysis, producing a solid-liquid separation. The clarified bottom layer or liquid phase (LP, 70% volume in manure and 65% in sludge), and the thickened top layer or solid phase (SP, 30% volume in manure and 35% in sludge) were digested separately. Operating at 37 °C, the time needed to digest the LP from manure was shorter (10 days) than that needed to digest the corresponding SP or the untreated substrate (22 days in both cases). The time needed to digest the separated phases of sludge (LP: 2 days, SP: 15 days) was lower than that needed to digest manure. Biogas production rates for the manure after pretreatment were 0.5 L/L·day for the SP and 0.7 L/L·day for the LP, allowing higher OLR (4.5-4.8 gCOD/L·day) than when digesting untreated manure and increasing biogas production by 17%. IPF applied to sewage sludge led to a production of 1.8 L/L·day at an OLR of 6.2 gCOD/L·day for the SP and 2.0 L/L·day at 12.9 gCOD/L·day for the LP. Assuming a conventional OLR of 2-3 gCOD/L·day, the advantage of applying IPF to sewage sludge resides in the possibility of operating digesters at much higher OLR.

Suburban air quality: Human health hazard assessment of potentially toxic elements in PM10

PM10 samples were collected at two suburban locations in northern Spain, a traffic-industrial suburban (TIS) station located in the coastal city of Gijón and an industrial suburban (IS) station in Langreo, about 25 km inland. The aerosol samples were chemically analysed to determine ambient air concentrations of As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Se, V and Zn. The results showed that the mean levels of As, Co, Cu, Fe, Mn, Ni, Pb and Se recorded at the IS location were higher than those at the TIS station. Mean levels of Fe and Zn in PM10 were higher than all other species at both the TIS and IS sampling sites (467 and 353 ng Fe/m³ and 46 and 282 ng Zn/m³, respectively). Human exposure to these twelve potentially toxic elements through PM10 was assessed for both children and adults using the U.S.EPA method, considering three pathways: ingestion, dermal contact and inhalation. In general, the IS location presented higher non-cancer risks than the TIS site. However, at both suburban locations, cancer and non-cancer risk values were in the acceptable range for adults, some exceptions being found. Greater health risk was estimated in the case of children. For this sector of the population, ingestion, dermal contact and/or inhalation of As, Pb and Zn in PM10 may pose a health hazard owing to possible carcinogenic/non-carcinogenic effects.

Impact of secondary inorganic aerosol and road traffic at a suburban air quality monitoring station

PM10 from a suburban site in the northwest of Spain was assessed using data from chemical determinations, meteorological parameters, aerosol maps and five-day back trajectories of air masses. Temporal variations in the chemical composition of PM10 were subsequently related to stationary/mobile local sources and long-range transport stemming from Europe and North Africa. The presence of secondary inorganic species (sulphates, nitrates and ammonium) in airborne particulate matter constituted one of the main focuses of this study. These chemical species formed 16.5% of PM10 on average, in line with other suburban background sites in Europe. However, a maximum of 47.8% of PM10 were recorded after several days under the influence of European air masses. Furthermore, the highest values of these three chemical species coincided with episodes of poor air circulation and influxes of air masses from Europe. The relationship between SO₄^2- and NH₄⁺ (R² = 0.57, p-value<0.01) was found to improve considerably in summer and spring (R² = 0.88 and R² = 0.87, respectively, p-value<0.01), whereas NO₃^- and NH₄⁺ (R² = 0.55, p-value<0.01) reproduced this pattern in winter (R² = 0.91, p-value<0.01). The application of a receptor model to the dataset led to the identification of notable apportionments due to road traffic and other types of combustion processes. In fact, large amounts of particulate matter were released to the atmosphere during episodes of biomass burning in forest fires. On isolated days, combustion was estimated to contribute up to 21.0 μg PM/m³ (50.8% of PM10). The contribution from industrial processes to this source is also worth highlighting given the presence of Ni and Co in its profile. Furthermore, African dust outbreaks at the sampling site, characterised by an arc through the Atlantic Ocean, were usually associated with a higher concentration of Al₂O₃ in PM10. Results evidenced the relevance of stationary (i.e., steelworks and thermal power station) and mobile sources in the air quality at the suburban site under study, with important apportionments of particulate matter coming from road traffic and as consequence of releasing precursor gases of secondary particles to the atmosphere.

Influence of the ultrasound pretreatment on anaerobic digestion of cattle manure, food waste and crude glycerine

To increase the production of methane, when cattle manure (CM) is digested, pretreatments can be applied and/or the manure can be co-digested with other wastes. In this research work, a mixture of CM, food waste (FW) and raw glycerine (Gly) in a proportion in weight of 87% CM, 10% FW and 3% Gly was digested, (a) without pretreatment and (b) with pretreatment by ultrasound, applying a sonication energy of 1040 kJ/kg total solids. Specific methane production was 290 L CH₄/kg volatile solids (VS) without pretreatment and 520 L CH₄/kg VS with pretreatment. With respect to the volumetric methane production, 1.07 L CH₄/L_reactor.day was produced in the first case, and in the second case, 1.98 L CH₄/L_reactor.day. We can conclude that the application of ultrasound pretreatment significantly improved the production of biogas.

Enrichment factors to assess the anthropogenic influence on PM10 in Gijón (Spain)

Thirty-two chemical species were determined in PM₁₀ sampled at a suburban site on the north coast of Spain. Enrichment factors were applied to infer their soil/non-soil origin. The geochemical ratios were calculated using two databases: soil composition from locations in the surroundings of the sampling station and the Earth's average upper-crust composition. In the present study, dissimilarities were found between the enrichment factors obtained using these two databases. Al, Ti, La and Ce were taken as the reference elements to normalise the data, reaching analogous conclusions. Bi, Cd, Cu, Sb, Se, Sn and Zn were associated with predominantly non-soil apportionments. As the relevance of soil/non-soil sources for the other analysed elements was found to be variable, they were probably of mixed origin. Furthermore, pairs of elements showed strong relationships, thus pointing to a common origin. Na-Mg and Co-Ni, with Pearson correlation coefficients above 0.9, were respectively related to marine and industrial apportionments. Enrichment factors have proved to be a useful tool to distinguish the soil/non-soil origin of chemical species present in airborne particulate matter. However, the choice of the reference database for soil composition considerably determined the accuracy of the conclusions.

Relationship between physico-chemical characteristics and potential toxicity of PM10

PM10 was sampled at a suburban location affected by traffic and industry in the north of Spain. The samples were analysed to determine the chemical components of PM10 (organic and elemental carbon, soluble chemical species and metals). The aim of this study was to assess the toxicity of PM10 in terms of the bulk analysis and the physico-chemical properties of the particles. Total carbon, sulphates, ammonium, chlorides and nitrates were found to be the major constituents of PM10. The contribution of the last of these was found to increase significantly with PM10 concentration (Pearson coefficient correlation of 0.7, p-value < 0.001). Individual airborne particles were characterised morphologically and chemically via a combination of Scanning Electron Microscopy and Energy-Dispersive X-ray spectroscopy (SEM-EDX). The subsequent image analysis revealed C-rich particles with shapes that pointed to combustion processes. Moreover, carbonaceous particles seemed to act as vehicles for sulphur compounds and metals (S, Na, Fe, Ca, Mg, K, Al, Mn, Zn and Cu). Coarse particles were found to be mainly constituted by crustal material and marine and carbonaceous particles. Although most of the studied individual particles in PM10 samples (86.0%) had a diameter within the 0.1-2.5 μm range, 1.8% of them had sizes lower than 0.1 μm 40.2% of the total studied particles were estimated to be inhaled and deposited in the human respiratory tract; 12.3% of these particles would reach the deepest zones, thereby posing a major risk to human health.

Traffic tracers in a suburban location in northern Spain: relationship between carbonaceous fraction and metals

PM10 and black smoke were monitored at a suburban sampling station located in the northern Spanish city of Gijón. Thirty-two metals and total carbon (TC) (i.e., organic carbon (OC) and elemental carbon (EC)) were analyzed over a year. The study of air-mass origin based on 5-day back trajectories was carried out to assess its influence on the recovery data. Different strategies were implemented to infer the influence of traffic in the area. On average, TC accounted for 29 % of the PM10 fraction, with OC forming 77 % of this TC. The influence of traffic was clearly reduced during intense Atlantic advection episodes, when OC and EC decreased up to 0.39 and 0.22 μg C/m(3), respectively. In contrast, the highest values were reported during regional episodes, exceeding 10 μg C/m(3) of OC and 2 μg C/m(3) of EC. The correlation between EC and OC was found to notably improve when considering the days with high traffic flow (from R (2) = 0.46 to R (2) = 0.74). This pattern was also reproduced by black smoke and EC (from R (2) = 0.49 to R (2) = 0.59). Cu and Sn were found to be reliable traffic tracers given their high dependence on EC (R (2) = 0.82 and R (2) = 0.79, respectively). Nevertheless, Sn, Ba, and Sb showed a better correlation with Cu than EC, suggesting a common origin. In the case of Sn, R (2) improved from 0.79 to 0.91. The Cu/Sb ratio had a mean value of 6.6 which agrees with diagnostic criterions for brake wear particles. The relationships and ratios between EC, Cu, Sb, Sn, Ba, and Bi pointed out to non-exhaust emissions, playing a significant role in the chemical composition of PM10. Brake wear was presented as the most likely origin for Cu, Sb, and Sn.

Differences in soluble COD and ammonium when applying inverted phase fermentation to primary, secondary and mixed sludge

Primary, secondary and mixed sludge were treated by inverted phase fermentation. This treatment results in solid-liquid separation of sludge after endogenous enzymatic hydrolysis (anaerobic conditions: 42°C, 48 hours). The soluble chemical oxygen demand (sCOD) was increased in the solid phase up to 1,800%, 21,300% and 260% in primary, secondary and mixed sludge, respectively. The corresponding increase in sCOD in the liquid phase accordingly reached values of up to 440%, 5,100% and 140%. Phase separation led to an enrichment of volatile solids in the solid phase (89-358% primary sludge, 80-102% secondary sludge and 29-133% mixed sludge). The NH4+-N values increased notably after the endogenous enzymatic hydrolysis itself. To investigate the short-term evolution following the treatment, the variation in sCOD, NH4+-N and solids was also monitored after keeping the hydrolysate at 37°C under anaerobic conditions for 24 hours. This stage showed no generalized pattern in terms of sCOD.

Differences in soluble COD and ammonium when applying ultrasound to primary, secondary and mixed sludge

Ultrasound treatment is often applied to enhance the anaerobic digestion of sludge. Optimal conditions for organic matter solubilisation of primary, secondary and mixed sludge were assessed by implementing ultrasound disruption at different specific energies (from 3,500 to 21,000 kJ/kgTS). The variation in soluble chemical oxygen demand (sCOD) and ammonium nitrogen (NH4+-N) was monitored following the treatment, and after a subsequent fermentation (24 h, 37 °C). The effect of the treatment was clearly more pronounced in secondary sludge than in the other types of sludge. Relatively minimal values in solubility were found when applying ultrasound at different energies depending on the sludge (3,500-7,000 kJ/kgTS in primary sludge and 10,500-14,000 kJ/kgTS in secondary sludge). This minimal value was not so noticeable in mixed sludge. The addition of inoculum was not required after ultrasound disruption in order to perform the subsequent fermentation. After this final stage, no general pattern in terms of sCOD was observed. Increases and decreases were conditioned by the coverage of the ultrasound irradiation; NH4+-N values increased notably during the fermentation.

Effect of ultrasound pre-treatment in the anaerobic co-digestion of cattle manure with food waste and sludge

This paper presents a study of the effect of applying ultrasound pre-treatment in the production of methane when co-digesting mixtures of cattle manure with food waste and sludge. A series of experiments were carried out under mesophilic and thermophilic conditions in continuously stirred-tank reactors containing 70% cattle manure, 20% food waste and 10% sewage sludge. Ultrasound pre-treatment allows operating at lower HRT, achieving higher volumetric methane yields: 0.85 L CH4/L day at 36°C and 0.82 CH4/L day at 55°C, when cattle manure and sewage sludge were sonicated. With respect to the non-sonicated waste, these values represent increases of up to 31% and 67% for mesophilic and thermophilic digestion, respectively.

Thermophilic co-digestion of cattle manure and food waste supplemented with crude glycerin in induced bed reactor (IBR)

The aim of the present research work was to boost biogas production from cattle manure (CM) by adding food waste (FW) and crude glycerin (Gly) from the biodiesel industry as co-substrates. For this purpose, different quantities of FW and Gly were added to CM and co-digested in an induced bed reactor (IBR) at 55 °C. Sonication pre-treatment was implemented in the CM+Gly mixture, applying 550 kJ/kg TS to enhance the biodegradability of these co-substrates. The best results were obtained with mixtures of 87/10/3 (CM/FW/Gly) (w/w) operating at an organic loading rate of 7 g COD/L day, obtaining 92% COD removal, a specific methane yield of 640 L CH4/kg VS and a methane production rate of 2.6L CH4/L day. These results doubled those obtained in the co-digestion of CM and FW without the addition of Gly (330 L CH4/kg VS and 1.2L CH4/L day).

A case study of the characteristics of municipal solid waste in Asturias (Spain): influence of season and source

In the present research study, the weight composition, physical-chemical composition and net calorific values of unsorted municipal solid waste (MSW) generated by a population of around 1,080,000 inhabitants in a region of northern Spain were determined. The unsorted MSW was composed of 38.1% organic fraction and 42.3% combustible fraction, with paper/cardboard constituting the most important part of the latter fraction (20.6%). The high content of textiles (10.9%) is worth noting, being practically equal to the content in plastics. The unsorted fractions present an average moisture content of 28.5% and an ash content of 29.4% (dry basis). The average lower heating value (LHV) is 10,744 kJ kg(-1). Likewise, variations in regard to the season of the year and the source of the waste were taken into consideration. A new correlation is proposed for estimating the LHV as a function of the physical composition of the waste.

Methane production from cattle manure supplemented with crude glycerin from the biodiesel industry in CSTR and IBR

The aim of the present research work was to optimise biogas production from cattle manure by adding crude glycerin from the biodiesel industry. For this purpose, 6%v/v crude glycerin (the optimum amount according to previous research) was added to ground manure and the mixture was sonicated to enhance biodegradability prior to anaerobic co-digestion at 55 °C. Two different reactors were used: continuously stirred (CSTR) and induced bed (IBR). The methanol and pure glycerin contents of the crude glycerin used in this study were 5.6% and 49.4% (w/w), respectively. The best results when operating in CSTR were obtained for an organic loading rate (OLR) of 5.4 kg COD/m(3) day, obtaining 53.2m(3) biogas/t wet waste and 80.7% COD removal. When operating in IBR, the best results were obtained for an OLR of 6.44 kg COD/m(3)day, obtaining 89.6% COD removal and a biogas production of 56.5m(3)/t wet waste.

Influence of conditioning agents and enzymic hydrolysis on the biochemical methane potential of sewage sludge

Biochemical methane potential (BMP) tests have been carried out on sewage sludge from two wastewater treatment plants to assess the effect of additives (FeCl(3) and two cationic polyelectrolytes) used in sludge dewatering. BMP tests were also carried out on the concentrated solid phase from the enzymic hydrolysis pre-treatment (42 °C, 48 h). FeCl(3) had no significant effect on specific methane production, obtaining 242-246 LCH(4)/kgVSo. The effect of the combination of polyelectrolyte and FeCl(3) depended on the polyelectrolyte and the sludge, but generally led to an increase in specific methane production (25-40%). When enzymic hydrolysis was applied as a pre-treatment, specific methane production increased from 6.8% in the sludge containing FeCl(3) to 20% in the sludge without FeCl(3), although the increases were not statistically significant. In terms of LCH(4)/kgVS(rem), a general improvement was achieved both by means of additives and by enzymic hydrolysis. However, this improvement was only significant in the case of sludge which had undergone previous enzymic hydrolysis (62%) and in the untreated sludge containing a polyelectrolyte and FeCl(3) (24%). Cationic polyelectrolytes inhibited solid-liquid separation during enzymic hydrolysis and, although the presence of only FeCl(3) did not affect this separation, a significant decrease (32%) in LCH(4)/kgVSrem was observed.

Co-digestion of cattle manure with food waste and sludge to increase biogas production

Anaerobic co-digestion strategies are needed to enhance biogas production, especially when treating certain residues such as cattle/pig manure. This paper presents a study of co-digestion of cattle manure with food waste and sewage sludge. With the aim of maximising biogas yields, a series of experiments were carried out under mesophilic and thermophilic conditions using continuously stirred-tank reactors, operating at different hydraulic residence times. Pretreatment with ultrasound was also applied to compare the results with those obtained with non-pretreated waste. Specific methane production decreases when increasing the OLR and decreasing HRT. The maximum value obtained was 603 LCH(4)/kg VS(feed) for the co-digestion of a mixture of 70% manure, 20% food waste and 10% sewage sludge (total solid concentration around 4%) at 36°C, for an OLR of 1.2g VS/L day. Increasing the OLR to 1.5g VS/L day led to a decrease of around 20-28% in SMP. Lower methane yields were obtained when operating at 55°C. The increase in methane production when applying ultrasound to the feed mixtures does not compensate for the energy spent in this pretreatment.

Optimization of biogas production from cattle manure by pre-treatment with ultrasound and co-digestion with crude glycerin

Biogas production by co-digestion of cattle manure with crude glycerin obtained from biodiesel production was studied after pre-treatment of the cattle manure or mixtures of cattle manure with different amounts of added glycerin with ultrasound. Batch experiments with 1,750 mL of medium containing 1,760 g of screened cattle manure or mixtures of cattle manure (screened or ground) and 70-140 mL or crude glycerin were incubated under mesophilic and thermophilic condition in stirred tank reactors. Under mesophilic conditions, the addition of 4% glycerin to screened manure increased biogas production by up to 400%. Application of sonication (20 kHz, 0.1 kW, and 4 min) to a mixture of manure+4% glycerin increased production of biogas by up to 800% compared to untreated manure. The best results were obtained under thermophilic conditions using sonicated mixtures of ground cattle manure with 6% added glycerin (348 L methane/kg COD removed were obtained).

Reducing the environmental impact of methane emissions from dairy farms by anaerobic digestion of cattle waste

Four dairy cattle farms considered representative of Northern Spain milk production were studied. Cattle waste was characterised and energy consumption in the farms was inventoried. Methane emissions due to slurry/manure management and fuel consumption on the farms were calculated. The possibility of applying anaerobic digestion to the slurry to minimise emissions and of using the biogas produced to replace fossil fuels on the farm was considered. Methane emissions due to slurry management (storage and use as fertiliser) ranged from 34 to 66kg CH(4)cow(-1)year(-1) for dairy cows and from 13 to 25kg CH(4)cow(-1)year(-1) for suckler calves. Cattle on these farms are housed for most of the year, and the contribution from emissions from manure dropped in pastures is insignificant due to the very low methane conversion factors. If anaerobic digestion were implemented on the farms, the potential GHG emissions savings per livestock unit would range from 978 to 1776kg CO(2)eq year(-1), with the main savings due to avoided methane emissions during slurry management. The methane produced would be sufficient to supply digester heating needs (35-55% of the total methane produced) and on-farm fuel energy requirements.

Colour, turbidity and COD removal from old landfill leachate by coagulation-flocculation treatment

The application of different coagulants and flocculants to leachate from an old landfill to determine the optimum conditions for removal of organic matter, colour and turbidity is studied. Ferric chloride, aluminium sulphate, aluminium polychloride (PAX) and polyacrylamide polyelectrolytes were tested. Higher pollutant removals (73% COD, 98% colour and 100% turbidity) were obtained using ferric chloride at pH 5.0-5.5 and for a dosage of 0.6 g Fe l(- 1). The volume of sludge generated after centrifugation represents about 4.0-4.6% when ferric chloride or aluminium sulphate is used, and 10% when employing aluminium polychloride. When flocculants were also added, the results obtained were similar to those found when adding only coagulants, although a considerable increase in the settling rate was obtained.

Physico-chemical analysis and calorific values of poultry manure

Spain is one of the major producers of broilers and laying hens in the European Union, with an overall market share of around 12%. The poultry manure that is produced is usually employed as fertilizer on cropland, either directly or after a composting process. In some cases, however, this waste is transported over 120km to be used as fertilizer, with the resulting high transport costs. In other countries, poultry manure is used as an alternative natural fuel source for power generation. In this study, poultry manure from all the laying hen farms in Asturias was characterized with a view to its possible use as an energy source. The Higher Heating Values on a dry basis (experimental) varies between 12,052 and 13,882kJ/kg. Lower Heating Values (LHVs) on a wet basis range are much lower (mean values of 2664kJ/kg) due to the high moisture content of poultry manure. Accordingly, the co-combustion of this waste with other types of waste such as forest and wood waste (LHV on a wet basis of 8044 and 15,830kJ/kg, respectively) or municipal solid waste (LHV on a wet basis of 10,725kJ/kg) should be considered as an alternative energy source. Chlorine and sulphur contents in dry matter vary around mean values of 0.64% and 0.11%, respectively. The waste also presents high amounts of Ca (4.84%) and K (2.38%).

Physico-chemical and biological treatment of MSW landfill leachate

This paper analyses the evolution of the physico-chemical characteristics of the leachate from the Central Landfill of Asturias (Spain), which has been operating since 1986, as well as different treatment options. The organic pollutant load of the leachate, expressed as chemical oxygen demand (COD), reached maximum values during the first year of operation of the landfill (around 80,000 mg/L), gradually decreasing over subsequent years to less than 5000 mg/L. The concentration of ammonium, however, has not decreased, presenting values of up to 2000 mg/L. When feasible, recirculation can greatly decrease the organic matter content of the leachate to values of 1500-1600 mg COD/L. Applying anaerobic treatment to leachates with a COD between 11,000 and 16,000 mg/L, removal efficiencies of 80-88% were obtained for organic loading rates of 7 kg COD/m3d. For leachates with lower COD (4000-6000 mg/L), the efficiency decreased to around 60% for organic loading rates of 1 kg COD/m3d. Applying coagulation-flocculation with iron trichloride or with aluminium polychloride, it was possible to reduce the non-biodegradable organic matter by 73-62% when treating old landfill leachate (COD: 4800 mg/L, BOD5: 670 mg/L), also reducing turbidity and colour by more than 97%. It is likewise possible to reduce the non-biodegradable organic matter that remains after biological treatment by adsorption with activated carbon, although adsorption capacities are usually low (from 15 to 150 mg COD/g adsorbent). As regards ammonium nitrogen, this can be reduced to final effluent values of 5 mg/L by means of nitrification/denitrification and to values of 126 mg/L by stripping at pH 12 and 48 h of stirring.

Denitrification of high nitrate concentration wastewater using alternative carbon sources

The use of different organic carbon sources in the denitrification of wastewater containing 2500 mg nitrates/L in a SBR was studied. Three alternative sources of carbon were tested: wastewater from a sweet factory, a residue from a soft drinks factory and a residue from a dairy plant. The first two are sugar-rich, whereas the third presents a high content in lactic acid. Maximum specific denitrification rates of between 42 and 48 mg NO(3)-N/g VSS h were obtained. The effluents were nitrate-free and very low COD concentrations were obtained in 4-6h reaction time, especially with the sugar-rich carbon sources. The values of the denitrifier net yield coefficient were higher than when using methanol (0.93-1.75 g VSS(formed)/g NO(x)-N(reduced)). The lowest value was obtained using the lactic acid-rich residue. The optimum COD/N ratios varied between 4.6 for the lactic acid-rich carbon source and 5.5-6.5 for the sugar-rich carbon sources.

Tertiary treatment of landfill leachates by adsorption

The leachates produced at the municipal solid waste (MSW) landfill of Asturias (Spain) were submitted to a biological treatment consisting of a pressurized nitrification-denitrification process followed by ultrafiltration. The effluent from this treatment plant has a high chemical oxygen demand : biochemical oxygen demand (COD : BOD( 5)) ratio (about 25 : 1). The COD values of the effluent are above the discharge limits permitted by current legislation and therefore require a final treatment. In the present study, adsorption was investigated as a possible post-treatment. Three activated carbons (Organosorb 10, Organosorb 10MB and Filtracarb CC65/1240) were selected and equilibrium and column data were obtained. The best results were obtained with Organosorb 10MB, although adsorption capacities obtained were low and equilibrium was unfavourable. Adsorption capacities ranged between 150 and 157 mg COD g(-1) for an activated carbon dosage of 1 mg L(-1) and between 13.3 and 18.4 mg COD g(-1) for a dosage of 20 mg L(-1). As regards colour, adsorption capacities ranged between 145 and 175 UPtCo g(-1) for the lower dosage and between 16 and 29 UPtCo g(-1) for the higher dosage. Removal efficiency increased with the dosage of activated carbon employed, obtaining maximum COD and colour removals of 63 and 45%, respectively, for a dosage of 20 mg L(-1) after 5 h contact time.

Anoxic-aerobic treatment of the liquid fraction of cattle manure

Cattle manure from a dairy farm was treated in order to reduce its pollution potential. The manure came from a farm with 120 cows kept in stables in a free stall barn. As pretreatment, the manure is usually filtered on the farm using a screw press separator with a 0.5 mm mesh. Approximately 70% of the total filtered volume passes through the screen, thus constituting the liquid fraction. This fraction, with a composition of around 64,500 mg COD/l, 5770 mg total-N/l and 800 mg total-P/l, was subjected to centrifugation followed by a two-step biological treatment (anoxic-aerobic) to reduce organic matter (COD), nitrogen and phosphorus compounds. Centrifugation led to the following removal efficiencies: 35% total solids, 60% COD, 75% total phosphorus and 20% total nitrogen (mainly organic nitrogen). With the subsequent anoxic-aerobic treatment, average removal efficiencies of 85% for COD, 90% for total phosphorus and 75% for total nitrogen were achieved.

Three-step biological process for the treatment of the liquid fraction of cattle manure

The liquid fraction of cattle manure was subjected to a biological treatment combining anoxic-anaerobic and oxic processes in order to stabilize the organic matter and reduce nitrogen and phosphorus so as to avoid problems of pollution when applying it to the land. The anoxic process was carried out at 30 degrees C in a CSTR reactor, the anaerobic process in a UASB reactor at 37 degrees C and the oxic treatment in another CSTR at 20 degrees C. The following results were obtained when working under optimum conditions (removal efficiencies in brackets): COD was reduced from 42 to 3.8 g/L (>90%); total solids from 41 to 14 (67%); total volatile solids from 22 to 7.0 (68%); total Kjeldahl nitrogen from 2.2 to 0.1 g/L (95%); NH4(-)-N from 1.10 to 0.02 g/L (98%) and Total-Phosphorus from 0.696 to 0.058 g/L (92%). Nitrates, undetected in the liquid fraction of cattle manure, were present in the final effluent as a result of nitrification. To reduce the amount of nitrates, different recirculation rates were tested. The minimum nitrate concentration achieved was 127 mg/L using a recirculation ratio of 4.

Denitrification of wastewater containing high nitrate and calcium concentrations

The removal of nitrate from rinse wastewater generated in the stainless steel manufacturing process by denitrification in a sequential batch reactor (SBR) was studied. Two different inocula from wastewater treatment plants were tested. The use of an inoculum previously acclimated to high nitrate concentrations led to complete denitrification in 6h (denitrification rate: 22.8mg NO3- -N/gVSSh), using methanol as carbon source for a COD/N ratio of 4 and for a content of calcium in the wastewater of 150mg/L. Higher calcium concentrations led to a decrease in the biomass growth rate and in the denitrification rate. The optimum COD/N ratio was found to be 3.4, achieving 98% nitrate removal in 7h at a maximum rate of 30.4mg NO3- -N/gVSSh and very low residual COD in the effluent.

Coagulation-flocculation as a pretreatment process at a landfill leachate nitrification-denitrification plant

The main aim of this research work was to study the possible application of coagulation-flocculation as a pretreatment process for young landfill leachate in order to prevent fouling in the ultrafiltration membranes employed for the separation of biomass in the biological plant. Jar-test experiments were carried out to determine the optimum conditions for the removal of turbidity colour and organic matter. The coagulants ferric chloride, aluminium sulphate and aluminium polychloride (PAX) were tested, along with different types of flocculants (anionic and cationic polyelectrolytes). Optimum pH values were around 4.0 and 6.0 for ferric chloride and aluminium sulphate, respectively. It was not necessary to alter the pH of the leachate when using PAX, as the optimum value was found to be similar to that of the leachate (around 8.3). Optimum dosages were 0.4 g Fe(3+)/L, 0.8 g Al(3+)/L and 4 g PAX/L, although there was not much difference in the results for lower dosage of PAX. The best results were found with this coagulant, obtaining 98% turbidity removal, 91% colour removal and 26% COD removal. When flocculants were also added, the results were similar to those found when adding only coagulants, although a considerable increase in the settling rate was obtained. The volume of the sludge generated represents around 4.5-5.0% when using ferric chloride or aluminium sulphate, and 15% when using aluminium polychloride.

Treatment of coke wastewater in a sequential batch reactor (SBR) at pilot plant scale

Coke wastewater is a highly toxic industrial effluent which is usually treated by a combination of physico-chemical and biological treatments. With the aim of completing prior studies carried out in CSTR, in this work we studied the treatment of coke wastewater in a pilot plant equipped with a 400 L stripping tank, a 350 L neutralization/homogenization tank and a 6 m high 1500 L sequential batch reactor (SBR), controlled by a PLC. Ammonia stripping efficiencies of 96% were obtained for HRT of 66 h. The biological treatment in the SBR led to removal efficiencies of 85% COD, 98% thiocyanate and 99% phenols for HRT of 115 h. Final concentrations in the effluent of 1.8 mg phenols/L, 5.4 mg SCN/L, 206 mg COD/L and 78 mg N-NH(4)(+)/L were obtained.

Removal of residual phenols from coke wastewater by adsorption

After biological treatment, coke wastewater contains small amounts of phenolic compounds resistant to such treatment. The removal of phenols and COD from coke wastewater subjected to biological treatment was studied. The adsorbents used were granular activated carbon and the resins XAD-2, AP-246 and OC-1074. Equilibrium, kinetics and column assays were carried out, fitting the equilibrium data to Langmuir and Freundlich models and the kinetic data to the Lagergren equation. The best results were obtained with GAC, which presented higher adsorption capacities. In the equilibrium assays, the adsorption capacities (Q) found were 1.48 mg g(-1) for GAC versus 0.07 and 0.04 mg g(-1) for resins AP-246 and OC-1074, respectively. In the kinetic assays, the values of the Lagergren adsorption parameter, q(e), were 1.69, 0.15 and 0.14 mg g(-1) for GAC, AP-246 and OC-1074, respectively. In the column assays, the dynamic capacity of GAC for up to 480 bed volumes was 1.82 mg mL(-1). No saturation was obtained for this volume due to the asymptotic shape of the breakthrough curve, whereas for the same percolated volume, the resins AP-246 and OC-1074 were saturated. These two resins presented similar saturation capacities of around 1.1 mg mL(-1).

Study of the aerobic biodegradation of coke wastewater in a two and three-step activated sludge process

A laboratory-scale biological plant composed of two aerobic reactors operating at 35 degrees C was used to study the biodegradation of coke wastewater. The main pollutants to be removed are organic matter, especially phenols, thiocyanate and ammonium nitrogen. The concentrations of the main pollutants in the wastewater during the study ranged between 922 and 1,980 mg COD/L, 133 and 293 mg phenol/L, 176 and 362 mg SCN/L and 123 and 296 mg NH(4)(+)-N/L. The biodegradation of these pollutants was studied employing different hydraulic residence times (HRT) and final effluent recycling ratios in order to minimize inhibition phenomena attributable to the high concentrations of pollutants. During the optimisation of the operating conditions, the removal of COD, phenols and thiocyanate was carried out in the first reactor and the nitrification of ammonium took place in the second. The best results were obtained when operating at an HRT of 98 h in the first reactor and 86 h in the second reactor, employing a recycling ratio of 2. The maximum removal efficiencies obtained were 90.7, 98.9, 98.6 and 99.9% for COD, phenols, thiocyanate and NH(4)(+)-N, respectively. In order to remove nitrate, an additional reactor was also implemented to carry out the denitrification process, adding methanol as an external carbon source. Very high removal efficiencies (up to 99.2%) were achieved.

Simultaneous removal of phenol, ammonium and thiocyanate from coke wastewater by aerobic biodegradation

A laboratory-scale activated sludge plant composed of a 20 L volume aerobic reactor followed by a 12 L volume settling tank and operating at 35 degrees C was used to study the biodegradation of coke wastewater. The concentrations of ammonium nitrogen (NH(4)(+) -N), phenols, chemical oxygen demand (COD) and thiocyanate (SCN(-)) in the wastewater ranged between 504 and 2,340, 110 and 350, 807 and 3,275 and 185 and 370 mg/L, respectively. The study was undertaken with and without the addition of bicarbonate. The addition of this inorganic carbon source was necessary to favour nitrification, as the alkalinity of the wastewater was very low. Maximum removal efficiencies of 75%, 98% and 90% were obtained for COD, phenols and thyocianates, respectively, without the addition of bicarbonate. The concentration of ammonia increased in the effluent due to both the formation of NH(4)(+) as a result of SCN(-) biodegradation and to organic nitrogen oxidation. A maximum nitrification efficiency of 71% was achieved when bicarbonate was added, the removals of COD and phenols being almost similar to those obtained in the absence of nitrification. Batch experiments were performed to study the influence of pH and alkalinity on the biodegradation of phenols and thiocyanate.

Removal of ammonium from aqueous solutions with volcanic tuff

This paper presents kinetic and equilibrium data concerning ammonium ion uptake from aqueous solutions using Romanian volcanic tuff. The influence of contact time, pH, ammonium concentration, presence of other cations and anion species is discussed. Equilibrium isotherms adequately fit the Langmuir and Freundlich models. The results showed a contact time of 3h to be sufficient to reach equilibrium and pH of 7 to be the optimum value. Adsorption capacities of 19 mg NH(4)(+)/g were obtained in multicomponent solutions (containing NH(4)(+), Zn(2+), Cd(2+), Ca(2+), Na(2+)). The presence of Zn and Cd at low concentrations did not decrease the ammonium adsorption capacity. Comparison of Romanian volcanic tuff with synthetic zeolites used for ammonium removal (5A, 13X and ZSM-5) was carried out. The removal efficiciency of ammonium by volcanic tuff were similar to those of zeolites 5A and 13X at low initial ammonium concentration, and much higher than those of zeolite ZSM-5.

Anaerobic mesophilic treatment of cattle manure in an upflow anaerobic sludge blanket reactor with prior pasteurization

Different autonomous communities located in northern Spain have large populations of dairy cattle. In the case of Asturias, the greatest concentration of dairy farms is found in the areas near the coast, where the elimination of cattle manure by means of its use as a fertilizer may lead to environmental problems. The aim of the present research work was to study the anaerobic treatment of the liquid fraction of cattle manure at mesophilic temperature using an upflow anaerobic sludge blanket (UASB) reactor combined with a settler after a pasteurization process at 70 degrees C for 2 hr. The manure used in this study came from two different farms, with 40 and 200 cows, respectively. The manure from the smaller farm was pretreated in the laboratory by filtration through a 1-mm mesh, and the manure from the other farm was pretreated on the farm by filtration through a separator screw press (0.5-mm mesh). The pasteurization process removed the pathogenic microorganisms lacking spores, such as Enterococcus, Yersinia, Pseudomonas, and coliforms, but bacterial spores are only reduced by this treatment, not removed. The combination of a UASB reactor and a settler proved to be effective for the treatment of cattle manure. In spite of the variation in the organic loading rate and total solids in the influent during the experiment, the chemical oxygen demand (COD) of the effluent from the settler remained relatively constant, obtaining reductions in the COD of approximately 85%.

Anaerobic treatment of sludge from a nitrification-denitrification landfill leachate plant

The viability of anaerobic digestion of sludge from a MSW landfill leachate treatment plant, with COD values ranging between 15,000 and 19,400mg O(2)dm(-3), in an upflow anaerobic sludge blanket reactor was studied. The reactor employed had a useful capacity of 9l, operating at mesophilic temperature. Start-up of the reactor was carried out in different steps, beginning with diluted sludge and progressively increasing the amount of sludge fed into the reactor. The study was carried out over a period of 7 months. Different amounts of methanol were added to the feed, ranging between 6.75 and 1cm(3)dm(-3) of feed in order to favour the growth of methanogenic flora. The achieved biodegradation of the sludge using an upflow anaerobic sludge blanket Reactor was very high for an HRT of 9 days, obtaining decreases in COD of 84-87% by the end of the process. Purging of the digested sludge represented approximately 16% of the volume of the treated sludge.

Removal of Cd and Zn from inorganic industrial waste leachate by ion exchange

This paper presents a study of the removal of Cd and Zn present in the leachate from an inorganic industrial waste landfill using cationic exchange resins (Amberlite 200, 252-C, IR-120, Duolite C-464), a chelating resin, Amberlite IRC 718, and an adsorbent resin, XAD-2. The chelating resin Amberlite IRC 718 presented the higher removal in batch experiments for both metals (93% for Zn and 50% for Cd). Five hundred ten bed volumes of leachate were treated in column experiments using this material, reducing the concentrations of Cd and Zn from 18 mg/dm3 to 0.1 and 1.0mg/dm3, respectively. Regeneration of the saturated bed was achieved with 11 BV of 2M HCl.

Ion exchange treatment of rinse water generated in the galvanizing process

A study was conducted of the viability of using the cationic exchange resins Amberlite IR-120 and Lewatit SP-112 to treat rinse water generated in the galvanizing process as well as acidic wastewater containing zinc (Zn) and iron (Fe). Solutions containing either 100 mg/L of Zn at pH 5.6 (rinse water) or Fe and Zn at concentrations of 320 and 200 mg/L at pH 1.5 (acidic water), respectively, were percolated through packed beds until the resins were exhausted. Breakthrough capacities obtained ranged between 1.1 and 1.5 meq metal/mL resin. The elution of metal and the regeneration of resins were performed with hydrochloric acid. The influence of the flowrate used during the loading stage was also studied, with 0.5 bed volumes/min (3.2 cm/min) found to be the optimum flowrate.

Extraction wells and biogas recovery modeling in sanitary landfills

A general methodology is established that permits the characterization and evaluation of the optimum potential of biogas extraction at each vertical well in the sanitary landfill of Asturias, Spain. Twenty wells were chosen from a total of 225 for the study, and the maximum production flow of biogas, which is a result of the degradation of the municipal solid waste deposited within its area of influence, was determined for each well. It was found that this flow varied with time and is characteristic of each extraction well. The maximum extractable flow also was determined as a function of the composition of the biogas needed for its subsequent utilization. The biogas extraction yield in the wells under study varied between approximately 26 and 97%, with a mean recovery value of 82%. The low yields found in certain cases were generally caused by a sealing defect, which leads to excessive incorporation of air into the landfill gas through the surrounding soil or through the extraction shaft, and which make its subsequent utilization difficult.

Removal of non-biodegradable organic matter from landfill leachates by adsorption

Leachates produced at the La Zoreda landfill in Asturias, Spain, were recirculated through a simulated landfill pilot plant. Prior to recirculation, three loads of different amounts of Municipal Solid Waste (MSW) were added to the plant, forming in this way consecutive layers. When anaerobic digestion was almost completed, the leachates from the landfill were recirculated. After recirculation, a new load of MSW was added and two new recirculations were carried out. The organic load of the three landfill leachates recirculated through the anaerobic pilot plant decreased from initial values of 5108, 3782 and 2560 mg/l to values of between 1500 and 1600 mg/l. Despite achieving reductions in the organic load of the leachate, a residual organic load still remained that was composed of non-biodegradable organic constituents such as humic substances. Similar values of the chemical oxygen demand (COD) were obtained when the landfill leachate was treated by a pressurised anoxic-aerobic process followed by ultrafiltration. After recirculation through the pilot plant, physico-chemical treatment was carried out to reduce the COD of the leachate. The pH of the leachate was decreased to a value of 1.5 to precipitate the humic fraction, obtaining a reduction in COD of about 13.5%. The supernatant liquid was treated with activated carbon and different resins, XAD-8, XAD-4 and IR-120. Activated carbon presented the highest adsorption capacities, obtaining COD values for the treated leachate in the order of 200mg/l. Similar results were obtained when treating with activated carbon, the leachate from the biological treatment plant at the La Zoreda landfill; in this case without decreasing the pH.

Life cycle analysis of Municipal Solid Waste management possibilities in Asturias, Spain

Directive 1994/62 concerning packaging and packaging waste and Directive 1999/31 related to waste disposal will substantially modify the management and treatment of Municipal Solid Waste (MSW) in Europe. In this study, a life cycle analysis has been carried out of the different possibilities of managing Municipal Solid Waste in Asturias. The "Integrated Waste Management" (IWM-1) model was employed, analysing the different alternatives for collection and treatment of MSW. This model predicts overall environmental burdens of MSW management systems and includes a parallel economical model. The sources of costs in the different systems of collection and treatment of MSW were considered in the economical analysis, as well as the sources of resource gathering that may be obtained via the sale of recovered materials. What emerges from this study is the soundness of management strategies based on biological treatment technologies in comparison with thermal treatments, together with the need to increase the level of collection at source.

Anaerobic thermophilic treatment of cattle manure in UASB reactors

Cattle manure was characterised after filtration through a 1-mm sieve and subsequently treated in a 9-l volume Upflow Anaerobic Sludge Blanket (UASB) reactor made of transparent PVC at a thermophilic temperature (55 degrees C). Different Hydraulic Retention Times (HRT) (22.5, 16, 10.6, 8.9 and 7.3 days) were employed and organic matter, total solids and metals were determined, as was the production of biogas. After screening, the COD of the manure subjected to anaerobic thermophilic treatment varied between values of 33,382 and 45,513 mgO2 l(-1). The highest percentage of COD removal obtained was 79.7% for an HRT of 22.5 days and there was a fraction refractory to biodegradation of 11%, calculated using Chen & Hashimoto's model. Finally, the results obtained at a thermophilic temperature were compared with those obtained at a mesophilic temperature (obtained in a previous work). The reduction in COD was slightly greater under mesophilic conditions, though the main advantage of thermophilic anaerobic treatment is the faster inactivation of viruses and bacteria.

The influence of hydraulic residence time on the treatment of cattle manure in UASB reactors

Cattle manure from farms in the autonomous community of Asturias, Spain, was characterised and subsequently treated, after filtration through a 1 mm sieve, in upflow anaerobic sludge blanket laboratory reactors. The volume generated per cow and day varied between 50-55 litres (obtained through a survey of 400 farms), the manure being used on Asturian farms up until now as a fertiliser. After screening, the COD of the manure employed varied between 33,000 and 56,000 mgO2 l(-1). The highest percentage of COD removal obtained was 75.5% for a hydraulic residence time of 22.5 days. Gas production varied between values of 0.20-0.39 m3gas kg(-1) COD removed, with a methane content of up to 64%. There was a fraction refractory to biodegradation of 11%.

Regulation of hepatic and non-hepatic apolipoprotein A-I and E gene expression during liver regeneration

In this study, we have determined what tissues other than liver express apolipoprotein (apo) A-I and apo E genes during liver regeneration at the level of the specific mRNAs, and have compared these findings with the serum values of high-density lipoprotein (HDL), low-density lipoprotein (LDL) and very-low-density lipoprotein (VLDL). Our results show that liver and intestine express most of the apo A-I mRNA during liver regeneration. Although apo E mRNA is expressed principally by the liver, its expression is reduced in liver during regeneration but is increased markedly in non-hepatic tissues, such as in intestine, kidney, lung and brain. These results suggest that humoral or circulating factors released during liver regeneration influence apolipoprotein E gene expression, not only in hepatic but also in non-hepatic tissue.

Regulation of apolipoprotein A-1 and E gene expression in liver and intestine of nephrotic and pair-fed rats

Rats treated with puromycin aminonucleoside (PAN) developed characteristics of the nephrotic syndrome, including albuminuria, hypoalbuminemia and hyperlipidemia. To study the regulation of apolipoprotein (apo) A-1 and apo E gene expression in nephrotic rats, we analyzed the steady-state levels (SSLs) of hepatic and intestinal apo A-1 and apo E mRNA using the Northern technique, and the plasma levels of high-density lipoprotein (HDL) by biochemical methods. Male Wistar rats were treated with PAN and compared with pair-fed and untreated control rats at different stages of disease. Nephrotic rats presented with marked hypoalbuminemia and albuminuria at between 6 and 11 days after PAN treatment. During this stage of disease, plasma levels of HDL were elevated in correlation with an increase of both hepatic and intestinal apo A-1 mRNA. In liver of nephrotic rats, high levels of apo A-1 mRNA together with low levels of apo E mRNA caused an increase in the ratio of apo A-1/apo E mRNA, reaching a maximum 6 days after treatment. Apo E mRNA was barely detected in small intestine of pair-fed controls and PAN-treated rats. However, contrary to nephrotic rats, the ratio apo A-1/apo E mRNA was inverted in liver of pair-fed rats due to an increase in apo E mRNA. In conclusion, in nephrotic rats, the SSL of apo A-1 mRNA is increased in liver and small intestine and appears to regulate the plasma levels of apo A-1. These results also suggest a coordinated regulation of the apo A-1 and apo E gene expression in liver of nephrotic and pair-fed rats.

Bacteriology of middle ear fluid specimens obtained by tympanocentesis from 111 Colombian children with acute otitis media

We cultured middle ear fluid specimens obtained by tympanocentesis from 111 Colombian infants and children, ages 11 days to 11 years, with acute otitis media. Bacteria were isolated in 82 patients (74%). Haemophilus influenzae, the most common isolate, was present in 40 cases (36%); 32 were nontypable strains and 8 were type b. Streptococcus pneumoniae, identified in 26 cases (22%), was the second most common pathogen. All H. influenzae and S. pneumoniae strains were susceptible to ampicillin and penicillin, respectively. We conclude that amoxicillin remains the drug of choice for treatment of acute otitis media in our country.