OPTIMAL MANAGEMENT OF A REGIONAL AQUIFER IN EASTERN SAUDI ARABIA1

ABSTRACT: This paper describes the formulation and application of a ground-water hydraulic management model to determine the optimal development and operating policies of a regional aquifer in the Eastern Province of Saudi Arabia. The hydraulic response of the aquifer system is represented by a simulation model that is linked to an optimization management model using response functions. Yearly optimal ground-water extraction rates over a planning horizon of 15 years are determined for four scenarios, each reflecting alternative ground-water development policies. The results are presented in the form of tradeoff curves, relating drawdowns to optimal pumpage, which may enhance the decisionmaker's ability to select the best development policy from a set of alternatives. The results illustrate how various optimal management schemes can be devised to increase the total withdrawal from the aquifer while preventing excessive de-watering.     

Biodegradability of degradable plastics exposed to anaerobic digested sludge and simulated landfill conditions

The biodegradabilities of various plastics by anaerobic digested sludge were measured and compared with the biodegradabilities under simulated landfill conditions. Bacterial poly(3-hydroxy-butyrate-co-3-hydroxyvalerate) (PHB/HV; 92/8, w/w), a natural aliphatic polyester, degraded nearly to completion within 20 days of cultivation by anaerobic digested sludge, while synthetic aliphatic polyesters such as poly-lactic acid, poly(butylene succinate), and poly (butylene succinate-co-ethylene succinate) did not degrade at all in 100 days. Cellophane, which was used as a control material, exhibited a similar degradation behavior to PHB/HV. Under simulated landfill conditions, PHB/HV degraded quite well within 6 months. Synthetic aliphatic polyesters also showed significant weight losses through 1 year of cultivation. The acidic environment inside simulators generated by the degradation of biodegradable food wastes which comprised 34 % of municipal solid waste seems to cause the weight loss of synthetic aliphatic polyesters.     

Heavy metal speciation in solid-phase materials from a bacterial sulfate reducing bioreactor using sequential extraction procedure combined with acid volatile sulfide analysis

Heavy metal mobility, bioavailability and toxicity depends largely on the chemical form of metals and ultimately determines potential for environmental pollution. For this reason, determining the chemical form of heavy metals and metalloids, immobilized in sludges by biological mediated sulfate reduction, is important to evaluate their mobility and bioavailability. A modified Tessier sequential extraction procedure (SEP), complemented with acid volatile sulfide (AVS) and simultaneous extracted metals (SEM) measurements, were applied to determine the partitioning of five heavy metals (defined as Fe, Ni, Zn and Cu, and the metalloid As) in anoxic solid-phase material (ASM) from an anaerobic, sulfate reducing bioreactor into six operationally defined fractions. These fractions were water soluble, exchangeable, bound to carbonates (acid soluble), bound to Fe-Mn oxides (reducible), bound to organic matter and sulfides (oxidizable) and residual. It was found that the distribution of Fe, Ni, Zn, Cu and As in ASM was strongly influenced by its association with the above solid fractions. The fraction corresponding to organic matter and sulfides appeared to be the most important scavenging phases of As, Fe, Ni, Zn and Cu in ASM (59.8-86.7%). This result was supported by AVS and SEM (Sigma Zn, Ni and Cu) measurements, which indicated that the heavy metals existed overwhelmingly as sulfides in the organic matter and sulfide fraction. A substantial amount of Fe and Ni at 16.4 and 20.1%, respectively, were also present in the carbonate fraction, while an appreciable portion of As (18.3%) and Zn (19.4%) was bound to Fe-Mn oxides. A significant amount of heavy metals was also associated with the residual fraction, ranging from 2.1% for Zn to 18.8% for As. Based on the average total extractable heavy metal (TEHM) values, the concentration of heavy metals in the ASM was in the order of Cu > Ni > Zn > Fe > As. If the mobility and bioavailability of heavy metals are assumed to be related to their solubility and chemical forms, and that they decrease with each successive extraction step, then the apparent mobility and bioavailability of these five heavy metals in ASM increase in the order of Cu < As < Ni < Fe < Zn. The SEM/AVS ratio was less than one in eight replicate ASM samples, indicating that the ASM was non-toxic with regards to having a low probability of bioavailable metals in the pore water.     

TWO PRACTICAL APPROACHES FOR DETERMINING THE CONFIDENCE INTERVAL OF RAINFALL DEPTH PERCENTILES1

ABSTRACT: A simple simulation type approach and a statistical method are proposed for determining the confidence interval of the T‐year frequency rainfall percentiles (or precipitation extremes) for generalized extreme value (GEV) distributions. The former method is based on the Monte Carlo testing procedure. To generate realizations, the covariance structure of the three parameters of GEV is investigated using an observed information matrix of the likelihood function. For distributions with realistic parameters, the correlation between the location and the scale parameters is practically constant when the shape parameter varies around values close to its optimal value. The latter method is based on likelihood ratio statistics. In the case where the joint confidence surface for shape parameters and estimates is plotted with lines of best estimates, the region where the estimated best percentile value can be chosen as a possible estimate is part of the joint confidence surface. The projection of this bounded region on axis of percentile is defined as the effective confidence interval in this research. The use of this effective interval as the confidence interval of the percentile of T‐year frequency rainfall is particularly recommended because it is stable for T and it reflects variations in all three parameters of GEV appropriately.     

Identification of Sources Contributing to Mid-Atlantic Regional Aerosol

Abstract

Source types or source regions contributing to the concentration of atmospheric fine particles measured at Brigantine National Wildlife Refuge, NJ, were identified using a factor analysis model called Positive Matrix Factorization (PMF). Cluster analysis of backward air trajectories on days of high- and low-factor concentrations was used to link factors to potential source regions. Brigantine is a Class I visibility area with few local sources in the center of the eastern urban corridor and is therefore a good location to study Mid-Atlantic regional aerosol. Sulfate (expressed as ammonium sulfate) was the most abundant species, accounting for 49% of annual average fine mass. Organic compounds (22%; expressed as 1.4 × organic carbon) and ammonium nitrate (10%) were the next abundant species. Some evidence herein suggests that secondary organic aerosol formation is an important contributor to summertime regional aerosol.

Nine factors were identified that contributed to PM_2.5 mass concentrations: coal combustion factors (66%, summer and winter), sea salt factors (9%, fresh and aged), motor vehicle/mixed combustion (8%), diesel/Zn-Pb (6%), incinerator/industrial (5%), oil combustion (4%), and soil (2%). The aged sea salt concentrations were highest in springtime, when the land breeze-sea breeze cycle is strongest. Comparison of backward air trajectories of high- and low-concentration days suggests that Brigantine is surrounded by sources of oil combustion, motor vehicle/mixed combustion, and waste incinerator/industrial emissions that together account for 17% of PM_2.5 mass. The diesel/Zn-Pb factor was associated with sources north and west of Brigantine. Coal combustion factors were associated with coal-fired power plants west and southwest of the site. Particulate carbon was associated not only with oil combustion, motor vehicle/mixed combustion, waste incinerator/industrial, and diesel/Pb-Zn, but also with the coal combustion factors, perhaps through common transport.     

Reduction of Waste and Electricity Demand in The Netherlands: A Hypothetical Intervention

An important question in the present reorganization and liberalization of infrastructure networks in many countries is what kind of regulatory regimes can provide incentives for demand management and reduction in a future situation. In this paper, the present situation in the Dutch waste and electricity sectors is analysed. It is concluded that a quantity-based tariff system and the entwined interests of organizations are key impediments to effective demand management in these two sectors. A hypothetical intervention is proposed which aims to remove these two fundamental drawbacks. Some likely consequences of the suggested intervention are discussed.     

Polychlorinated biphenyls,polycyclic aromatic hydrocarbons and alkylphenols in sediments from the Odra River and its tributaries,Poland

Concentrations of polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), nonylphenol (NP) and octylphenol (OP) were measured in sediments collected during June–August 1998 along the Odra River and its tributaries (Warta, Obrzyca, Barycz, Kaczawa and Bóbr Rivers) in Poland. In addition, raw and treated sewage sludge collected from Gdańsk, Poland, were analyzed for the target compounds. Concentrations of PCBs in sediments varied widely, ranging from 2.7 to 412?ng/g, on a dry weight basis (dry wt). PAHs were the predominant compounds in sediments with concentrations ranging from 150 to 19?000?ng/g, dry wt. The distribution of concentrations of PAHs was more homogenous than that of PCBs. NP concentrations in sediments ranged from <1 to 762?ng/g, while that of OP from <1 to 9.8?ng/g, dry wt. Measured concentrations of target analytes in sediments of the Odra River and its tributaries were comparable to or greater than those reported for riverine sediments in other eastern European countries. Concentrations of total PCBs, PAHs and NP in raw and treated sewage sludge collected from a sewage treatment plant in Gdańsk, Poland, were in the ranges of 203–284, 11?720–13?880 and 6760–99?600?ng/g, dry wt, respectively. Primary treatment of sewage did not appear to reduce PCB or PAH concentrations, although NP and OP concentrations were much less in treated sludge than in raw sludge. This is one of a few studies that document concentrations of PCBs, PAHs and NP in sediments of the Odra River and its tributaries in Poland.