Noninformative trends in natural resource commodity prices: U-shaped price paths exonerated

M. J. Mueller and D. R. Gorin (J. Environ. Econ. Manag.12, 83–89 (1985)) claim that the U-shaped price paths found in M. E. Slade (J. Environ. Econ. Manag.9, 122–137 (1982a)) result from a misspecification and disappear when the equation is properly specified. To produce their result, they rely on a radical shift in technology that is claimed to have occurred in 1920. There is, however, no evidence of a technology shift in that year. Instead, a gradual adoption of new mining techniques beginning in 1904 is seen. In addition to this misspecification, they incorrectly locate other exogenous influences such as wars and recessions. When corrections are made, a radically different picture emerges. With the new equation, the U-shaped price pattern persists, and the only exogenous influence that is consistently insignificant is the technology shift.     

Trends in natural-resource commodity prices: An analysis of the time domain

This paper attempts to reconcile the theoretical predictions of increasing real prices for nonrenewable natural-resource commodities obtained from Hotelling-style models with the empirical findings of falling prices for these commodities. A theoretical model for relative-price movements is derived for the case of exogenous technical change and endogenous change in the grade of ores mined. The model suggests a U-shaped time path for relative prices. The implied price movements are tested for all the major metals and fuels and the model parameters are found to be statistically significant for 11 out of the 12 commodities tested.     

An econometric model of the U.S. secondary copper industry: Recycling versus disposal

In this paper, a theoretical model of secondary recovery is developed that integrates microeconomic theories of production and cost with a dynamic model of scrap generation and accumulation. The model equations are estimated for the U.S. secondary copper industry and used to assess the impacts that various policies and future events have on copper recycling rates. The alternatives considered are: subsidies for secondary production, differing energy costs, and varying ore quality in primary production.     

Technological options for the management of biosolids

BACKGROUND, AIM, AND SCOPE: Large quantities of biosolids (sewage sludge), which are produced from municipal wastewater treatment, are ever-increasing because of the commissioning of new treatment plants and continuous upgrades of the existing facilities. A large proportion of biosolids are currently landfilled. With increasing pressure from regulators and the general public, landfilling of biosolids is being phased out in many countries because of potential secondary pollution caused by leachate and the emission of methane, a potent greenhouse gas. Biosolids contain nutrients and energy that can be used beneficially. Significant efforts have been made recently to develop new technologies to manage biosolids and make useful products from them. In this paper, we provide a review of the technologies in biosolids management. MATERIALS AND METHODS: A survey of literature was conducted. RESULTS: At present, the most common beneficial use of biosolids is agricultural land application because of inherent fertilizer values found in biosolids. Expansion of land application, however, may be limited in the future because of more stringent regulatory requirements and public concern about food chain contamination in some countries. Perceived as a green energy source, the combustion of biosolids has received renewed interest. Anaerobic digestion is generally a more effective method than incineration for energy recovery, and digested biosolids are suitable for further beneficial use through land application. Although conventional incineration systems for biosolid management generally consume more energy than they produce because of the high moisture content in the biosolids, it is expected that more combustion systems, either monocombustion or cocombustion, will be built to cope with the increasing quantity of biosolids. DISCUSSION: Under the increasingly popular low-carbon economy policy, biosolids may be recognized as a renewable fuel and be eligible for 'carbon credits'. Because ash can be used to manufacture construction materials, combustion can provide a complete management for biosolids. A number of advanced thermal conversion technologies (e.g., supercritical water oxidation process and pyrolysis) are under development for biosolids management with a goal to generate useful products, such as higher quality fuels and recovery of phosphorus. With an ever-increasing demand for renewable energy, growing bioenergy crops and forests using biosolids as a fertilizer and soil amendment can not only contribute to the low-carbon economy but also maximize the nutrient and carbon value of the biosolids. CONCLUSIONS: Land application of biosolids achieves a complete reuse of its nutrients and organic carbon at a relatively low cost. Therefore, land application should become a preferred management option where there is available land, the quality of biosolids meet regulatory requirements, and it is socially acceptable. Intensive energy cropping and forest production using biosolids can help us meet the ever-increasing demand for renewable energy, which can eliminate the contamination potential for food sources, a common social concern about land application of biosolids. In recent years, increasing numbers of national and local governments have adopted more stringent regulations toward biosolid management. Under such a political climate, biosolids producers will have to develop multireuse strategies for biosolids to avoid being caught because a single route management practice might be under pressure at a short notice. Conventional incineration systems for biosolids management generally consume more energy than they produce and, although by-products may be used in manufacturing, this process cannot be regarded as a beneficial use of biosolids. However, biosolids are likely to become a source of renewable energy and produce 'carbon credits' under the increasingly popular, low-carbon economy policy. RECOMMENDATIONS AND PERSPECTIVES: To manage biosolids in a sustainable manner, there is a need for further research in the following areas: achieving a higher degree of public understanding and acceptance for the beneficial use of biosolids, developing cost-efficient and effective thermal conversions for direct energy recovery from biosolids, advancing technology for phosphorus recovery, and selecting or breeding crops for efficient biofuel production.     

The effects of higher energy prices and declining ore quality: Copper—aluminium substitution and recycling in the USA

An econometric model of the US copper and aluminium industries is simulated to evaluate the impact that higher energy prices and declining ore quality will have on copper–aluminium substitution and recycling in the USA in the next decade. The unique features of the model described here include the calculation of elasticities of substitution between copper and aluminium from the production functions of the using sectors, the use of statistical (not engineering) cost functions for both the primary and the secondary industries, and the explicit consideration of ore- quality deterioration as primary production progresses.     

Impact of sampling techniques on measured stormwater quality data for small streams

Science-based sampling methodologies are needed to enhance water quality characterization for setting appropriate water quality standards, developing Total Maximum Daily Loads, and managing nonpoint source pollution. Storm event sampling, which is vital for adequate assessment of water quality in small (wadeable) streams, is typically conducted by manual grab or integrated sampling or with an automated sampler. Although it is typically assumed that samples from a single point adequately represent mean cross-sectional concentrations, especially for dissolved constituents, this assumption of well-mixed conditions has received limited evaluation. Similarly, the impact of temporal (within-storm) concentration variability is rarely considered. Therefore, this study evaluated differences in stormwater quality measured in small streams with several common sampling techniques, which in essence evaluated within-channel and within-storm concentration variability. Constituent concentrations from manual grab samples and from integrated samples were compared for 31 events, then concentrations were also compared for seven events with automated sample collection. Comparison of sampling techniques indicated varying degrees of concentration variability within channel cross sections for both dissolved and particulate constituents, which is contrary to common assumptions of substantial variability in particulate concentrations and of minimal variability in dissolved concentrations. Results also indicated the potential for substantial within-storm (temporal) concentration variability for both dissolved and particulate constituents. Thus, failing to account for potential cross-sectional and temporal concentration variability in stormwater monitoring projects can introduce additional uncertainty in measured water quality data.     

Recent advances in econometric estimation of materials substitution

Interest in substituting reproducible inputs such as capital and labour for non-renewable materials is principally motivated by two factors — the short-run concern about supply disruptions on the part of producing countries and the long-run concern about the exhaustion of depletable natural resources. In this paper, techniques for estimating elasticities of substitution between inputs (ie between different materials or between material aggregates and other input aggregates) from production and cost functions are discussed, and the recent literature that makes use of these techniques is reviewed.     

Cycles in natural-resource commodity prices: An analysis of the frequency domain

A model is derived that relates price cycles to investment behavior in the mineral industries and predicts that these cycles will be roughly twice as long as the investment period (the period between the investment decision and the project completion). Spectral techniques are used to estimate the principal cycles in metal and fuel prices. For the metals, the estimated cycle lengths reinforce the model predictions. However, no significant cycles are found in the prices of the fuels. The lead-lag relationships between prices of different commodities are also investigated and are found to be significant for those that are jointly produced.