Energy implications of the thermal recovery of biodegradable municipal waste materials in the United Kingdom

Waste management policies and legislation in many developed countries call for a reduction in the quantity of biodegradable waste landfilled. Anaerobic digestion, combustion and gasification are options for managing biodegradable waste while generating renewable energy. However, very little research has been carried to establish the overall energy balance of the collection, preparation and energy recovery processes for different types of wastes. Without this information, it is impossible to determine the optimum method for managing a particular waste to recover renewable energy. In this study, energy balances were carried out for the thermal processing of food waste, garden waste, wood, waste paper and the non-recyclable fraction of municipal waste. For all of these wastes, combustion in dedicated facilities or incineration with the municipal waste stream was the most energy-advantageous option. However, we identified a lack of reliable information on the energy consumed in collecting individual wastes and preparing the wastes for thermal processing. There was also little reliable information on the performance and efficiency of anaerobic digestion and gasification facilities for waste.     

The effect of mercury on trees and their mycorrhizal fungi

The Oak Ridge Reservation, established in 1942, was the designated site for the construction of the atomic bomb. During a 20-year period from 1944 to 1963 radioactive and toxic chemical pollutants, especially mercury compounds were released into the surrounding waterways. Tree diversity and mycorrhizal presence and abundance were analyzed in the mercury-contaminated floodplains of East Fork Poplar Creek Oak Ridge (EFPC) (Tennessee). A subsequent greenhouse study was conducted to assess the phytotoxic effects of different mercuric solutions on Platanus occidentalis (American Sycamore), inoculated with soils from EFPC. Total soil mercury in the field had no effect on tree diversity. Organic species of mercury proved to be more toxic than inorganic species of mercury and soil inoculants from EFPC had no protective effects against Hg toxicity in our greenhouse study. Comparison of the effects of mercury contamination in our field and greenhouse studies was difficult due to uncontrolled factors.     

Wastewater Effluent,Combined Sewer Overflows,and Other Sources of Organic Compounds to Lake Champlain1

Abstract: Some sources of organic wastewater compounds (OWCs) to streams, lakes, and estuaries, including wastewater‐treatment‐plant effluent, have been well documented, but other sources, particularly wet‐weather discharges from combined‐sewer‐overflow (CSO) and urban runoff, may also be major sources of OWCs. Samples of wastewater‐treatment‐plant (WWTP) effluent, CSO effluent, urban streams, large rivers, a reference (undeveloped) stream, and Lake Champlain were collected from March to August 2006. The highest concentrations of many OWCs associated with wastewater were in WWTP‐effluent samples, but high concentrations of some OWCs in samples of CSO effluent and storm runoff from urban streams subject to leaky sewer pipes or CSOs were also detected. Total concentrations and numbers of compounds detected differed substantially among sampling sites. The highest total OWC concentrations (10‐100 μg/l) were in samples of WWTP and CSO effluent. Total OWC concentrations in samples from urban streams ranged from 0.1 to 10 μg/l, and urban stream‐stormflow samples had higher concentrations than baseflow samples because of contributions of OWCs from CSOs and leaking sewer pipes. The relations between OWC concentrations in WWTP‐effluent and those in CSO effluent and urban streams varied with the degree to which the compound is removed through normal wastewater treatment. Concentrations of compounds that are highly removed during normal wastewater treatment [including caffeine, Tris(2‐butoxyethyl)phosphate, and cholesterol] were generally similar to or higher in CSO effluent than in WWTP effluent (and ranged from around 1 to over 10 μg/l) because CSO effluent is untreated, and were higher in urban‐stream stormflow samples than in baseflow samples as a result of CSO discharge and leakage from near‐surface sources during storms. Concentrations of compounds that are poorly removed during treatment, by contrast, are higher in WWTP effluent than in CSO, due to dilution. Results indicate that CSO effluent and urban stormwaters can be a significant major source of OWCs entering large water bodies such as Burlington Bay.     

Response of methane emission to invasion of Spartina alterniflora and exogenous N deposition in the coastal salt marsh

Spartina alterniflora exhibits great invading potential in the coastal marsh ecosystems. Also, nitrogen (N) deposition shows an apparent increase in the east of China. To evaluate CH₄ emissions in the coastal marsh as affected by the invasion of S. alterniflora and N deposition, we measured CH₄ emission from brackish marsh mesocosms vegetated with S. alterniflora and a native plant, Suaeda salsa, and fertilized with exogenous N at the rates of 0 and 2.7 g N m^?2, respectively. Dissolved porewater CH₄ concentration and redox potentials in soils as well as aboveground biomass and stem density of plants were also monitored. The averaged rate of CH₄ emission during the growing season in the S. alterniflora and S. salsa mesocosms without N application was 0.88 and 0.54 mg CH₄ m^?2 h^?1, respectively, suggesting that S. alterniflora plants significantly increased CH₄ emission mainly because of higher plant biomass rather than stem density compared to S. salsa, which delivered more substrates to the soil for methanogenesis. Exogenous N input dramatically stimulated CH₄ emission by 71.7% in the S. alterniflora mesocosm. This increase was attributable to enhancement in biomass and particularly stem density of S. alterniflora driven by N application, which transported greater photosynthesis products than oxygen into soils for CH₄ production and provided more pathways for CH₄ emission. In contrast, there was no significant effect of N fertilization on CH₄ emission in the S. salsa mesocosm. Although N fertilization significantly stimulated CH₄ production by increasing S. salsa biomass, no significant increase in stem density was observed. This fact, along with the low gas transport capacity of S. salsa, failed to efficiently transport CH₄ from wetlands into the atmosphere. Thus we argue that the stimulatory or inhibitory effect of N fertilization on CH₄ emission from wetlands might depend on the gas transport capacity of plants and their relative contribution to substrates for CH₄ production and oxygen for CH₄ oxidation in soil.     

Eco-certification of Farmed Seafood: Will it Make a Difference?

Eco-certification is widely considered a tool for reducing environmental impacts of aquaculture, but what are the likely environmental outcomes for the world’s fastest growing animal-food production sector? This article analyzes a number of eco-certification schemes based on species choice, anticipated share of the global seafood market, size of eligible producers, and targeted environmental impacts. The potential of eco-certification to reduce the negative environmental impacts of aquaculture at scale presently appears uncertain as: (a) certification schemes currently focus on species predominantly consumed in the EU and US, with limited coverage of Asian markets; (b) the share of certified products in the market as currently projected is too low; (c) there is an inequitable and non-uniform applicability of certification across the sector; (d) mechanisms or incentives for improvement among the worst performers are lacking; and (e) there is incomplete coverage of environmental impacts, with biophysical sustainability and ecosystem perspectives generally lacking.     

SITE Demonstration of the Basic Extractive Sludge Treatment Process

The Superfund Innovative Technology Evaluation (SITE) Program, in cooperation with EPA Region 5, the Great Lakes National Program Office (GLNPO), and the U.S. Army Corps of Engineers (COE) planned and executed a pilot-scale evaluation of the Basic Extractive Sludge Treatment (B.E.S.T.®) process on sediment samples obtained from the Grand Calumet River in Gary, Indiana. Two separate sampling locations were selected based upon previous data. One location had sediments with total polychlorinated biphenyl (PCB) concentrations averaging 10 mg/kg, and total polynuclear aromatic hydrocarbon (PAH) concentrations averaging 520 mg/kg. The other location had sediments with average total PCB and PAH concentrations of 427 mg/kg and 72,000 mg/kg, respectively. The sediment samples were segregated by location, then screened, homogenized, and stored prior to treatment. A total of ten batches of sediments were treated (five for each sample location).

Results showed that of the samples which had low original contaminants concentrations, 96 percent of the PAHs and >99 percent of the PCBs were removed following seven sequential extractions. Treated samples which had high original contaminant concentrations were found to have removal efficiencies of >99 percentfor both PAHs and PCBs. Costs for applying this technology were estimated at $94.19/ton (assuming the system is on-line 80 percent of the time) excluding fixed costs associated with system mobilization/ demobilization and setup, and profit.     

Behaviour and dynamics of di-ammonium phosphate in bauxite processing residue sand in Western Australia—I. NH<Subscript>3</Subscript> volatilisation and residual nitrogen availability

Background, aim and scope

Australia is the largest producer of bauxite in the world, with an annual output of approximately 62 million metric dry tons in 2007. For every tonne of alumina, about 2 tonnes of highly alkaline and highly saline bauxite-processing residue are produced. In Western Australia, Alcoa World Alumina, Australia (Alcoa) produces approximately 15 MT of residue annually from its refineries (Kwinana, Pinjarra and Wagerup). The bauxite-processing residue sand (BRS) fraction represents the primary material for rehabilitating Alcoa’s residue disposal areas (RDAs). However, the inherently hostile characteristics (high alkalinity, high salinity and poor nutrient availability) of BRS pose severe limitations for establishing sustainable plant cover systems. Alcoa currently applies 2.7 t ha^?1 of di-ammonium phosphate ((NH₄)₂HPO₄; DAP)-based fertiliser as a part of rehabilitation of the outer residue sand embankments of its RDAs. Limited information on the behaviour of the dominant components of this inorganic fertiliser in highly alkaline BRS is currently available, despite the known effects of pH on ammonium (NH₄) and phosphorus (P) behaviour. The aim of this study was to quantify the effects of pH on NH₃ volatilisation and residual nitrogen (N) in BRS following DAP applications.

Methods

The sponge-trapping and KCl-extraction method was used for determining NH₃ volatilisation from surface-applied DAP in samples of BRS collected from each of Alcoa’s three Western Australia Refineries (Kwinana, Pinjarra, Wagerup) under various pH conditions (pH 4, 7, 9 and 11). Following cessation of volatilisation, the residual N was extracted from BRS using 2 M KCl and concentrations of NH ₄ ⁺ –N and NO ₃ ^? –N were determined by flow injection analysis.

Results

The quantities of NH₃ volatilised increased dramatically as the pH increased from 4 to 11. Much of the N lost as NH₃ (up to 95.2%) occurred within a short period (24 h to 7 days), particularly for the pH 9 and 11 treatments. Concentrations of residual NH ₄ ⁺ –N recovered in DAP-treated BRS at the end of the experiment decreased with increasing pH. This finding was consistent with increasing loss of N via volatilisation as pH increased. The concentration of NO ₃ ^? –N was very low due to no nitrification in BRS.

Discussion

The pH was a key driver for NH₃ volatilisation from DAP-treated BRS and primarily controlled N dynamics in BRS. Results indicate that NH₄ not adsorbed by BRS was highly susceptible to volatilisation. The likely lack of nitrifying bacteria did not allow conversion of ammonium to nitrate, thereby further exacerbating the potential for loss via volatilisation

Conclusions

It was demonstrated that the pH is the key factor controlling the loss of inorganic N from BRS. Although volatilisation was considerably lower at pH 4, achieving this pH reduction in the field is not possible at present. Findings from this study highlight the need to better understand which forms of N fertiliser are most suitable for use in highly alkaline BRS.

Recommendation and perspectives

Although pH reduction is the most likely means of stopping NH₃ volatilisation in BRS, it is economically and operationally unfeasible to add sufficient acidity for adequately lowering pH in the BRS for revegetation. More attention on forms of fertilisers more suitable to highly alkaline, microbially inert soil conditions appears to be warranted.

     

Limited occurrence of denitrification in four shallow aquifers in agricultural areas of the United States

The ability of natural attenuation to mitigate agricultural nitrate contamination in recharging aquifers was investigated in four important agricultural settings in the United States. The study used laboratory analyses, field measurements, and flow and transport modeling for monitoring well transects (0.5 to 2.5 km in length) in the San Joaquin watershed, California, the Elkhorn watershed, Nebraska, the Yakima watershed, Washington, and the Chester watershed, Maryland. Ground water analyses included major ion chemistry, dissolved gases, nitrogen and oxygen stable isotopes, and estimates of recharge date. Sediment analyses included potential electron donors and stable nitrogen and carbon isotopes. Within each site and among aquifer-based medians, dissolved oxygen decreases with ground water age, and excess N(2) from denitrification increases with age. Stable isotopes and excess N(2) imply minimal denitrifying activity at the Maryland and Washington sites, partial denitrification at the California site, and total denitrification across portions of the Nebraska site. At all sites, recharging electron donor concentrations are not sufficient to account for the losses of dissolved oxygen and nitrate, implying that relict, solid phase electron donors drive redox reactions. Zero-order rates of denitrification range from 0 to 0.14 micromol N L(-1)d(-1), comparable to observations of other studies using the same methods. Many values reported in the literature are, however, orders of magnitude higher, which is attributed to a combination of method limitations and bias for selection of sites with rapid denitrification. In the shallow aquifers below these agricultural fields, denitrification is limited in extent and will require residence times of decades or longer to mitigate modern nitrate contamination.     

Comparison of aerobic and anaerobic biotreatment of municipal solid waste

To increase the operating lifetime of landfills and to lower leachate treatment costs, an increasing number of municipal solid waste (MSW) landfills are being managed as either aerobic or anaerobic bioreactors. Landfill gas composition, respiration rates, and subsidence were measured for 400 days in 200-L tanks filled with fresh waste materials to compare the relative effectiveness of the two treatments. Tanks were prepared to provide the following conditions: (1) air injection and leachate recirculation (aerobic), (2) leachate recirculation (anaerobic), and (3) no treatment (anaerobic). Respiration tests on the aerobic wet tank showed a steady decrease in oxygen consumption rates from 1.3 mol/day at 20 days to 0.1 mol/day at 400 days. Aerobic wet tanks produced, on average, 6 mol of carbon dioxide (CO2)/kg of MSW as compared with anaerobic wet tanks, which produced 2.2 mol methane/kg of MSW and 2.0 mol CO2/kg methane. Over the test period, the aerobic tanks settled on average 35%, anaerobic tanks settled 21.7%, and the no-treatment tank settled 7.5%, equivalent to overall mass loss in the corresponding reactors. Aerobic tanks reduced stabilization time and produced negligible odor compared with anaerobic tanks, possibly because of the 2 orders of magnitude lower leachate ammonia levels in the aerobic tank. Both treatment regimes provide the opportunity for disposal and remediation of liquid waste.