Column Flotation Deinking: State-of-the-art and opportunities

Flotation is a critical process step for ink removal from recycled paper. Column flotation is a specific form of flotation that has grown in popularity recently. Extensive efforts during the past four decades to improve the flotation deinking operation sought an optimum blend of technological parameters, physico-chemical aspects and economical process conditions. With increasing demand to recover and recycle waste paper due to ecological and economical concerns, there is a need for an improved process and therefore for in-depth understanding of the mechanism and fundamental factors involved in the efficiency and economics of the deinking process. This paper reviews the progress made in the last decade (2000–2010) in deinking hydrodynamics, various measurement techniques, scale-up and design criterion.     

Analysis of Scavengers’ Activities and Recycling in Some Cities of Nigeria

The state of solid waste recycling by scavengers in Onitsha, a heavily commercial city in Anambra State, and some other urban areas such as Nsukka, Enugu, and Port Harcourt was analyzed. Data were obtained through interviews of scavengers who deal with recyclables. Although the activities of scavengers are sub-optimal, they can have a great impact on Nigerian economy with respect to resource conservation, creation of job opportunities, and reduction of the magnitude of waste disposal problems. A cost analysis is presented to compare the different forms of recycling utilized by municipal solid waste management. It is shown that a well-planned recycling program with recycling and composting would result in 18.6% savings in waste management costs and 57.7% in landfill avoidance costs. However, if the compost materials are not recycled, the corresponding savings in cost become 8.6% and 28.6%, respectively. The option with the lowest cost involves encouraging individual households to separate at the source their recyclables, which are bought by scavengers. This results in 78.0% savings in waste management cost and 79.5% landfill avoidance cost. A low-cost approach aimed at the integration of scavenging activities into conventional solid waste management is presented.     

The effects of recovering fibre and fine materials on sludge dewatering properties at a deinked pulp mill

The manufacture of deinked pulp generates large amounts of waste for disposal. The yield loss in the production of recycled paper can be up to 25%. The use of landfills for waste disposal is very expensive and will be prohibited in Europe in the next few years. Thus, there is a great pressure to improve the material efficiency and to reduce the amount of waste that is produced at deinked pulp mills. However, the issue is complex because an improvement of the material efficiency at one process unit may deteriorate the performance of other stages. For example, the attempts to increase the fibre yield in the deinking processes can lead to poor sludge dewatering properties, resulting in that there are no added advantages for the mill anymore.This work aims to determine the limitations between the sludge dewatering properties and the improvements in material efficiency at a deinked pulp mill by investigating the dewatering properties of sludge samples that contained variable amounts of fine screening and flotation froth rejects. The results show that the deinked pulp mill material efficiency can be increased without weakening the sludge dewatering properties if the fibre content is not reduced below a certain limit. The material efficiency can be increased either by (1) recovering fibres at an acceptable quantity where the fibre content does not decrease below the limiting point or by (2) recovering fine materials simultaneously with fibres in a way that maintains the fibre content above a limiting point. The first method provides an opportunity for deinking mills to increase the yield, even though the increase is less than 2 percentage units. With the simultaneous recovery of fibres and fine materials using the second method, it would be possible to improve the material efficiency at the deinked pulp mill by approximately 5 percentage units without affecting the dewatering of the combined sludge.     

Ferric-manganese doped sulphated zirconia nanoparticles catalyst for single-step biodiesel production from waste cooking oil: Characterization and optimization

Biodiesel of waste cooking oil origin is gaining attention as a replacement for current fossil fuels, as its low-priced, recycled feedstock shall prevent food source competition, which is estimated to happen with current biodiesel production processes. As a result, waste cooking oil has been claimed to be a highly potential feedstock for biodiesel production. In the present research work, Fe-Mn doped sulphated zirconia catalyst was synthesized and used in simultaneous esterification and transesterification of waste cooking oil to biodiesel synthesis. The catalyst was prepared through the impregnation method and characterized by using XRD, TPD-NH_3, FT-IR, BET, and TEM. Response surface methodology (RSM) in conjunction with the central composite design (CCD) was applied to statistically evaluate and optimize the biodiesel preparation process. It was found that the synthesis of biodiesel achieved an optimum level of 97.2% waste cooking oil methyl ester’s (WCOME’s) yield at the following reaction conditions: methanol/oil molar ratio: 10:1, catalyst concentration: 3.0 wt %, and reaction temperature: 160 °C. The extremely high WCOME’s yield of 97.2% was proved to be due to high acidity, surface area, and large pore diameter; reactants can easily diffuse into the interior pore of the catalyst and allow them to be in contact with active sites that enhance catalytic activity.     

Immersion frying for the thermal drying of sewage sludge: an economic assessment

This paper presents an economic study of a novel thermal fry-drying technology which transforms sewage sludge and recycled cooking oil (RCO) into a solid fuel. The process is shown to have significant potential advantage in terms of capital costs (by factors of several times) and comparable operating costs. Three potential variants of the process have been simulated and costed in terms of both capital and operating requirements for a commercial scale of operation. The differences are in the energy recovery systems, which include a simple condensation of the evaporated water and two different heat pump configurations. Simple condensation provides the simplest process, but the energy efficiency gain of an open heat pump offset this, making it economically somewhat more attractive. In terms of operating costs, current sludge dryers are dominated by maintenance and energy requirements, while for fry-drying these are comparatively small. Fry-drying running costs are dominated by provision of makeup waste oil. Cost reduction could focus on cheaper waste oil, e.g. from grease trap waste.     

A Systems Approach to Materials Flow in Sustainable Cities: A Case Study of Paper

This study develops a modelling framework within which the effects of technology choice and policy on the sustainability of cities may be assessed. A life cycle accounting system for environmental impacts is combined with systems analysis, to represent the flows of resources into cities, the wastes and pollution generated and the technological choices available in an urban environment. The approach is demonstrated through a case study of the demand for paper and management of wastepaper. The case study questions the applicability for paper of the accepted 'hierarchy' of waste management techniques; incineration imposes lower environmental costs than recycling, and consequently lower total costs under some circumstances.     

Determining the socially optimal recycling rate

What municipal recycling rate is socially optimal? One credible answer would consider the recycling rate that minimizes the overall social costs of managing municipal waste. Such social costs are comprised of all budgetary costs and revenues associated with operating municipal waste and recycling programs, all costs to recycling households associated with preparing and storing recyclable materials for collection, all external disposal costs associated with waste disposed at landfills or incinerators, and all external benefits associated with the provision of recycled materials that foster environmentally efficient production processes. This paper discusses how to estimate these four components of social cost to then estimate the optimal recycling rate.     

Toxic releases from paper made with recovered wastepaper versus virgin wood fiber: A research note

Toxic Release Inventory (TRI) data were used to compare average releases (kilograms per metric ton) of paper mills using primarily recovered wastepaper versus mills using primarily virgin wood fiber. Annual releases, for 79 mills, of chlorine, chlorine dioxide, chloroform, acids (hydrochloric and sulfuric), volatile organics (methyl ethyl ketone, methanol, and acetone), and ammonia were compared over the years 1987–1992. Both types of mills reported generally lower toxic releases in 1992 than in 1987; however, toxic releases in all categories were significantly lower from mills using recovered wastepaper than from mills using virgin wood fiber, strongly demonstrating that recycling has added benefits beyond reduced resource consumption. These results suggest that environmental policy should concentrate as much on increasing demand for recycled paper and developing wastepaper collection infrastructure as it does on end-of-pipe pollution abatement.     

A system dynamics model for evaluating the alternative of type in construction and demolition waste recycling center - The case of Chongqing, China

This paper presents a system dynamics computer model to evaluate alternative type of recycling center under different policy and economy environments through comparison on the economic feasibility of recycling centers and ratio of savings to costs in C&D waste management. A case study for the City of Chongqing, China is selected. Simulated results show three key factors can contribute to the economic feasibility of recycling and the ratio of savings to costs in C&D waste management: (a) profit; (b) unit recycling cost; (c) extra revenue from location advantage (It was assumed that the mobile centers can attain extra revenue from the location advantage compared with fixed recycling centers). The sensitive analysis and comparison on ratios between public and private sector indicate that to achieve the optimum ratio of savings to costs, design of recycling centers and selection of governmental instruments are determined by the priority list: (1) low extra revenue from location advantage; (2) low profit; (3) low unit recycling cost. Meanwhile, the fluctuation of the three factors must be prior to achieve economic feasibility of corresponding recycling centers.     

The costs and benefits of packaging waste management systems in Europe: the perspective of local authorities

Local authorities are generally in charge of household packaging waste management operations, particularly in countries with Green Dot schemes or similar extended producer responsibility systems. This leads to the need of establishing a system of financial transfers between the packaging industry and the local authorities (regarding the costs involved in selective collection and sorting). In the present study, the costs and benefits of recycling, from the perspective of local authorities, are compared for Portugal, Belgium and Italy (in Lombardia region), adopting the same economic–financial methodology. The results show that the industry is not paying the net cost of packaging waste management. If the savings attained by diverting packaging waste from other treatment operations are not considered, it seems that the industry should increase the financial support to local authorities. However, if the avoided costs with other treatments are considered as a benefit for local authorities, the costs are generally outweighed by the benefits, and the financial support could, therefore, be reduced.     

MONITORING AND CONTROL OF CENTER PIVOT SYSTEMS WITH MICROCOMPUTERS1

A computerized water-energy-management system (WEMS) can be used by center pivot operators to reduce pumping fuel costs and monitoring expenses. Irrigation costs are lowered primarily because the system used climatic data and plant growth models to derive water schedules that considerably lowers the use of water compared with conventional irrigation practices. A capital budget analysis of a hypothetical, but representative farm growing corn, shows that cost savings are from three sources: 61 percent from pumping less water, 28 percent from labor savings, and 11 percent from savings on truck fuel, maintenance, and oiL The analysis illustrates that only a 4 percent water savings from irrigation scheduling over a 10-year period is required for the investment to be profitable for many central High Plains’ irrigators. The water savings required are relatively small compared with the potentials shown by irrigation scheduling research. WEMS is cost effective and can extend the life of the ground water source.     

Leaching characteristics of copper flotation waste before and after vitrification

Copper flotation waste from copper production using a pyrometallurgical process contains toxic metals such as Cu, Zn, Co and Pb. Because of the presence of trace amounts of these highly toxic metals, copper flotation waste contributes to environmental pollution. In this study, the leaching characteristics of copper flotation waste from the Black Sea Copper Works in Samsun, Turkey have been investigated before and after vitrification. Samples obtained from the factory were subjected to toxicity tests such as the extraction procedure toxicity test (EP Tox), the toxicity characteristic leaching procedure (TCLP) and the "method A" extraction procedure of the American Society of Testing and Materials. The leaching tests showed that the content of some elements in the waste before vitrification exceed the regulatory limits and cannot be disposed of in the present form. Therefore, a stabilization or inertization treatment is necessary prior to disposal. Vitrification was found to stabilize heavy metals in the copper flotation waste successfully and leaching of these metals was largely reduced. Therefore, vitrification can be an acceptable method for disposal of copper flotation waste.     

Amounts of non-fibrous components in recovered paper

Paper and board recycling is now a central issue in papermaking. Understanding of material flows, as a part of the total production chain, as well as, fibrous and non-fibrous component flows needs further clarification. These flows are studied at a European level, with special focus on Germany and Sweden. Non-fibrous components are discussed in terms of a material which hampers the processing of paper and board. Resource-efficiency improvements, in conjunction with economic benefits, are sought and recycling has been able to fulfil both of these. The main drivers to maximize the use of recovered paper in paper and board manufacturing, have been improved over the last decades. These drivers are cost, environmental image and good technical properties to be used as raw material.The increased recycling rate has reduced the quality of the collected paper, produced recycled paper, and replaced virgin pulp. Also, recycling as a process, like deinking, produces large amounts of waste material that has challenges to find proper utilization. These problem areas are addressed in this paper, too.One focus area in the analysis of statistical information is an estimation of the share of non-fibrous components and fibre volumes of paper in Europe (EU) for the year 2010.     

填料式浮选柱操作参数的研究

在实验室装置上研究了不锈钢波纹板填料柱的主要操作参数对除油率的影响。研究结果表明：填料可以明显改善气体在柱内的径向分布，可以明显提高浮选柱的操作稳定性。实验确定了波纹板填料式浮选柱的主要操作参数是：最低气体表现线速度3．8cm／s，污水停留时间为5min，浮选剂投加量为5～10mg／L。     

Is Municipal Solid Waste Recycling Economically Efficient?

It has traditionally been argued that recycling municipal solid waste (MSW) is usually not economically viable and that only when externalities, long-term dynamic considerations, and/or the entire product life cycle are taken into account, recycling becomes worthwhile from a social point of view. This article explores the results of a wide study conducted in Israel in the years 2000–2004. Our results reveal that recycling is optimal more often than usually claimed, even when externality considerations are ignored. The study is unique in the tools it uses to explore the efficiency of recycling: a computer-based simulation applied to an extensive database. We developed a simulation for assessing the costs of handling and treating MSW under different waste-management systems and used this simulation to explore possible cost reductions obtained by designating some of the waste (otherwise sent to landfill) to recycling. We ran the simulation on data from 79 municipalities in Israel that produce over 60% of MSW in Israel. For each municipality, we were able to arrive at an optimal method of waste management and compare the costs associated with 100% landfilling to the costs born by the municipality when some of the waste is recycled. Our results indicate that for 51% of the municipalities, it would be efficient to adopt recycling, even without accounting for externality costs. We found that by adopting recycling, municipalities would be able to reduce direct costs by an average of 11%. Through interviews conducted with representatives of municipalities, we were also able to identify obstacles to the utilization of recycling, answering in part the question of why actual recycling levels in Israel are lower than our model predicts they should be.     

Who will pay? Subsidies or taxes for recycling in the heartland

Attaining recycling goals of 25 to 50% over the next few years will require substantial recycling of residential wastes. A combined program of curbside recycling of conventional post-consumer materials and collection and composting of both leaves and grass will yield a composite diversion rate of 12 to 21% by weight. But in many communities, particularly in the west central and south central states of the American heartland, implementation of such programs will result in a net increase in solid waste management costs. Case studies of four communities in Oklahoma are used to estimate the potential increase in first-year net costs that would result from implementing a combined recycling and yard waste composting program. The results are compared to survey data from Oklahoma and Florida that define the amount residents are likely to be willing to pay for the benefits of recycling. The potential to close the apparent willingness-to-pay gap through state subsidies is then assessed. Where state capital grants programs are insufficient to bridge the gap, and local officials are reluctant to impose costs that are not publicly supported, public education efforts will be needed to increase the value residents ascribe to the nonexclusive positive externalities and local nonmarket benefits of recycling.     

A review on the use of waste glasses in the production of cement and concrete

The use of recycled waste glasses in Portland cement and concrete has attracted a lot of interest worldwide due to the increased disposal costs and environmental concerns. Being amorphous and containing relatively large quantities of silicon and calcium, glass is, in theory, pozzolanic or even cementitious in nature when it is finely ground. Thus, it can be used as a cement replacement in Portland cement concrete. The use of crushed glasses as aggregates for Portland cement concrete does have some negative effect on properties of the concrete; however, practicle applicability can still be produced even using 100% crushed glass as aggregates. The main concerns for the use of crushed glasses as aggregates for Portland cement concrete is the expansion and cracking caused by the glass aggregates. This paper summarizes the progresses and points out the directions for the proper uses of waste glasses in Portland cement and concrete.     

Can oligopsony power be measured? The case of U.S. old newspapers market

This paper uses an index analogous to Lerner-index in the input market to derive a price–cost margin that measures input exploitation by few large buyers. This paper identifies oligopsony characteristics associated with the old newspaper (ONP) input market for recycled-content newsprint manufacture and then examines the impacts of market performances on ONP input prices. The wastepaper recycling market, in particular, ONP has not been successful in utilizing the ONP generated. The existence of high sunk costs for entry to the market, along with the small numbers of buyers in the old newspapers market, were the reasons to believe that the waste paper industry had oligopsony elements among paper recycling mills. The regional oligopsony/oligopoly indices were derived and the impact of these market powers on ONP input prices were examined for period 1972–1995. The findings of this study were: oligopsony elements were present to certain degrees among the recycled-content newsprint manufacturers; and the oligopsony market power enabled these mills to exert a larger price–cost margin on ONP input market.     

Concrete block production from construction and demolition waste in Tanzania

In Tanzania, construction and demolition (C&D) waste is not recycled and knowledge on how it can be recycled especially into valuable products like building materials are still limited. This study aimed at investigating the possibility of recycling the C&D waste (mainly cementitious rubble) into building material in Tanzania. The building materials produced from C&D waste was concrete blocks. The concrete blocks were required to have a load bearing capacity that meets the building material standards and specifications. Eight C&D waste samples were collected from C&D building sites, transported to the recycling site, crushed, and screened (sieved) to get the required recycled aggregates. Natural aggregates were also used as control. The recycled aggregates were tested in the laboratory following the standard methods as specified in Tanzanian standards. The physical, mechanical and chemical characteristics were determined. The physical and mechanical results showed that recycled aggregates were weaker than natural aggregates. However, chemically they were close to natural aggregates and therefore suitable for use in new concrete block production. In the production process, each experiment utilized 100% recycled aggregates for both fine and coarse portions to replace natural aggregates. The Fuller's maximum density theory was used to determine the mix proportions of materials in which a method that specifies concrete mix by system of proportion or ratio was used. The concrete blocks production processes included batching, mixing (that was done manually to get homogeneous material), compacting and moulding by hand machine and curing in water. After 28 days of curing, the concrete blocks were tested in the laboratory on compressive strength, water absorption ratio and density. The results showed that the blocks produced with 100% recycled aggregates were weaker than those with natural aggregates. However, the results also showed that there is a possibility of recycling the C&D waste into building material because 85% of the tested concrete block specimens from recycled aggregates achieved a compressive strength of 7 N/mm², which is defined as the minimum required load bearing capacity in Tanzania. Therefore, the C&D waste could be a potential resource for building material production for sustainable construction in Tanzania rather than discarding it. Further work should focus on the economic feasibility of production of concrete blocks with recycled aggregates in Tanzania.     

氨法在烧结烟气脱硫中的应用

在钢铁工业排放的污染物中，烧结烟气中的二氧化硫和焦化废氨水等都是难以处理的污染物。利用焦化废氨水吸收烧结烟气中SO2的氨一硫铵工艺具有脱硫率高、运行可靠、投资低、副产品可以回收等优点，在脱硫的同时也去除了焦化废水中的氨污染，是一种以废治废、有应用前景的新方法。本文介绍了采用焦化废氨水吸收烧结烟气中的SO2的治污方法原理，并对其工艺流程、特点及运行费用等作了分析。