An overview of waste materials recycling in the Sultanate of Oman

Various wastes and by-product materials are generated in the Sultanate of Oman including reclaimed asphalt pavement (RAP) aggregate, demolition concrete, cement by-pass dust (CBPD), copper slag, petroleum-contaminated soils (PCS), discarded tires, incinerator ash, and others. Recycling of such materials in construction is not practiced. Research data are also minimal into the potential use of selected materials in construction applications. This paper will present the results of several laboratory studies conducted into the use of PCS in asphalt concrete mixtures; on the use of CBPD in soil stabilization and flowable fill mixtures; on the utilization of copper slag and CBPD as cementitious materials; on the use of incinerator ash in cement mortars; and on the use of RAP aggregate in road bases and sub-bases. Laboratory data generally indicate that it is feasible to partially reuse some of these materials in construction provided that economic incentives and environmental concerns are taken into consideration.     

Utilization of cement kiln dust (CKD) in cement mortar and concrete—an overview

Solid waste management is one of the major environmental concerns around the world. Cement kiln dust (KKD), also known as by-pass dust, is a by-product of cement manufacturing. The environmental concerns related to Portland cement production, emission and disposal of CKD is becoming progressively significant. CKD is fine-grained, particulate material chiefly composed of oxidized, anhydrous, micron-sized particles collected from electrostatic precipitators during the high temperature production of clinker. Cement kiln dust so generated is partly reused in cement plant and landfilled. The beneficial uses of CKD are in highway uses, soil stabilization, use in cement mortar/concrete, CLSM, etc.Studies have shown that CKD could be used in making paste/mortar/concrete. This paper presents an overview of some of the research published on the use of CKD in cement paste/mortar/concrete. Effect of CKD on the cement paste/mortar/concrete properties like compressive strength, tensile strength properties (splitting tensile strength, flexural strength and toughness), durability (Freeze–thaw), hydration, setting time, sorptivity, electrical conductivity are presented. Use of CKD in making controlled low-strength materials (CLSM), asphalt concrete, as soil stabilizer, and leachate analysis are also discussed in this paper.     

水泥注浆中六价铬总溶出量的影响因素研究

水泥注浆过程中析出液中的六价铬Cr(Ⅵ)易造成地下水的重金属污染,对生态和环境具有较大危害性,为了有效降低水泥注浆中Cr(Ⅵ)总溶出量,采用化学还原的方法,探讨了各种降铬剂及其掺量对降低Cr(Ⅵ)总溶出量的效果,研究了颗粒粒度、液固比对Cr(Ⅵ)总溶出量的影响.结果 表明,硫酸亚铁降铬剂的效果最显著,当用量在3％以内时...     

Utilization of cement kiln dust (CKD) in cement mortar and concrete—an overview

Solid waste management is one of the major environmental concerns around the world. Cement kiln dust (KKD), also known as by-pass dust, is a by-product of cement manufacturing. The environmental concerns related to Portland cement production, emission and disposal of CKD is becoming progressively significant. CKD is fine-grained, particulate material chiefly composed of oxidized, anhydrous, micron-sized particles collected from electrostatic precipitators during the high temperature production of clinker. Cement kiln dust so generated is partly reused in cement plant and landfilled. The beneficial uses of CKD are in highway uses, soil stabilization, use in cement mortar/concrete, CLSM, etc.Studies have shown that CKD could be used in making paste/mortar/concrete. This paper presents an overview of some of the research published on the use of CKD in cement paste/mortar/concrete. Effect of CKD on the cement paste/mortar/concrete properties like compressive strength, tensile strength properties (splitting tensile strength, flexural strength and toughness), durability (Freeze–thaw), hydration, setting time, sorptivity, electrical conductivity are presented. Use of CKD in making controlled low-strength materials (CLSM), asphalt concrete, as soil stabilizer, and leachate analysis are also discussed in this paper.     

Life cycle climate impacts of the US concrete pavement network

Life cycle assessment (LCA) offers a comprehensive approach to evaluate and improve the environmental impacts of pavements. First, a general pavement LCA methodology is created that describes the concepts necessary to conduct a comprehensive pavement LCA. Second, the methodology is applied to the life cycle of concrete pavements to quantify current emissions across the road network. System boundaries are drawn to include all phases of the pavement life cycle – materials production, construction, use, maintenance, and end of life. Greenhouse gas emissions are quantified for twelve functional units, which evaluate average conditions for each major roadway classification in the United States. The results present the relative contribution of each component in the life cycle, the annual emissions occurring during the 40-year analysis period, and the sensitivity of these results to model parameters. It is found for all roads that the majority of emissions occur in year one – from cradle-to-gate materials production, and pavement construction – primarily due to cement production. The results are most sensitive to traffic volume, and then to parameters affecting the cement production. Based on emissions and their sensitivity, the LCA results suggest three broad reduction approaches: reducing embodied emissions, reducing use phase emissions, and reducing end-of-life emissions.     

A Side‐by‐Side Comparison of Pervious Concrete and Porous Asphalt1

Welker, Andrea L., James D. Barbis, and Patrick A. Jeffers, 2012. A Side‐by‐Side Comparison of Pervious Concrete and Porous Asphalt. Journal of the American Water Resources Association (JAWRA) 48(4): 809‐819. DOI: 10.1111/j.1752‐1688.2012.00654.x Abstract: This article compares the performance of two permeable pavements, pervious concrete and porous asphalt, that were installed side‐by‐side in fall 2007. Because the pavements are located directly adjacent to one another, they experience the same vehicle loads, precipitation, and pollution loads. These permeable pavements are part of an infiltration stormwater control measure (SCM). This article focuses on the comparison of water quality parameters, maintenance and durability, and user perception. Eleven different water quality parameters were analyzed at this site for 19 different storm events over a one year period: pH, conductivity, total suspended solids, chlorides, total nitrogen, total phosphorus, total dissolved copper, total dissolved lead, total dissolved cadmium, total dissolved chromium, and total dissolved zinc. Results from the two pavement types were compared using the Mann–Whitney U‐test. The only parameter that was found to be statistically different between the two pavements was pH. Periodic inspection of the two pavement types indicated that after two years of use both pavements were wearing well. However, there was some evidence of clogging of both pavements and some evidence of surface wear. A survey of users of the lot indicated that the perception of these permeable pavements was favorable.     

Study on recycled asphalt concrete for use in surface course in airport pavement

This research investigated the possibility of using recycled asphalt concrete as surface course in airport pavement. The basic properties of recycled asphalt binder after short- and long-term aging were firstly tested and compared with those of the virgin asphalt. Then, a series of laboratory tests were performed to evaluate the performance of recycled asphalt concrete (containing 40% and 70% RAP), in which the HMA mixture without RAP was used as a control. Furthermore, an experimental pavement consisting of three sections (corresponding to 0%, 40% and 70% RAP content) was constructed to verify the laboratory test results. These results indicated that the recycled asphalt could achieve the similar properties against long-term aging as virgin asphalt. Recycled asphalt concrete containing 40% RAP could be used as surface course in airport pavement as it exhibited similar performance as control mixture both from the laboratory and experimental pavement test results. On the contrary, recycled asphalt concrete containing 70% RAP was not recommended as its fatigue property was much poorer compared with that of virgin asphalt mixture.     

Size distributions of manure particles released under simulated rainfall

Manure and animal waste deposited on cropland and grazing lands serve as a source of microorganisms, some of which may be pathogenic. These microorganisms are released along with particles of dissolved manure during rainfall events. Relatively little if anything is known about the amounts and sizes of manure particles released during rainfall, that subsequently may serve as carriers, abode, and nutritional source for microorganisms. The objective of this work was to obtain and present the first experimental data on sizes of bovine manure particles released to runoff during simulated rainfall and leached through soil during subsequent infiltration. Experiments were conducted using 200 cm long boxes containing turfgrass soil sod; the boxes were designed so that rates of manure dissolution and subsequent infiltration and runoff could be monitored independently. Dairy manure was applied on the upper portion of boxes. Simulated rainfall (ca. 32.4 mm h(-1)) was applied for 90 min on boxes with stands of either live or dead grass. Electrical conductivity, turbidity, and particle size distributions obtained from laser diffractometry were determined in manure runoff and soil leachate samples. Turbidity of leachates and manure runoff samples decreased exponentially. Turbidity of manure runoff samples was on average 20% less than turbidity of soil leachate samples. Turbidity of leachate samples from boxes with dead grass was on average 30% less than from boxes with live grass. Particle size distributions in manure runoff and leachate suspensions remained remarkably stable after 15 min of runoff initiation, although the turbidity continued to decrease. Particles had the median diameter of 3.8 microm, and 90% of particles were between 0.6 and 17.8 microm. The particle size distributions were not affected by the grass status. Because manure particles are known to affect transport and retention of microbial pathogens in soil, more information needs to be collected about the concurrent release of pathogens and manure particles during rainfall events.     

AN OVERVIEW OF POROUS PAVEMENT RESEARCH1

ABSTRACT: This paper discusses the economics, advantages, potential applications, and status and future research needs of porous pavements. Porous pavements are an available storm water management technique which can be used on parking lots and low volume roadways in order to reduce both storm water runoff volume and pollution. In addition, ground water recharge is enhanced. Also, cost reductions result due to elimination of curbs, drains, and small sized storm sewers. Porous asphalt pavements consist of a relatively thin course of open graded asphalt mix over a deep base of large size crushed stones. Water can be stored in the crushed stone base until it can percolate into the subbase or drain laterally. Other porous pavement types include concrete lattice blocks and a porous concrete mix.     

Evaluating phosphorus loss from a Florida spodosol as affected by phosphorus-source application methods

Incorporating applied phosphorus (P) sources can reduce P runoff losses and is a recommended best management practice. However, in soils with low P retention capacities, leaching can be a major mechanism for off-site P loss, and the P-source application method (surface or incorporation) may not significantly affect the total amount of off-site P loss. We utilized simulated rainfall protocols to investigate effects of P-source characteristics and application methods on the forms and amounts of P losses from six P sources, including five biosolids materials produced and/or marketed in Florida, and one inorganic fertilizer (triple superphosphate). A typical Florida Spodosol (Immokalee fine sand; sandy, siliceous, hyperthermic Arenic Alaquods) was used for the study, to which the P sources were each applied at a rate of 224 kg P ha(-1) (approximately the P rate associated with N-based biosolids applications). The P sources were either surface-applied to the soil or incorporated into the soil to a depth of 5 cm. Amended soils were subjected to three simulated rainfall events, at 1-d intervals. Runoff and leachate were collected after each rainfall event and analyzed for P losses in the form of soluble reactive P (SRP), total dissolved P (TDP), total P (TP), and bioavailable P (BAP) (in runoff only). Cumulative masses (runoff + leachate for the three rainfall events) of P losses from all the P sources were similar, whether the amendments were surface-applied or incorporated into the soil. The solubility of the amendment, rather than application method, largely determines the P loss potential in poorly P-sorbing Florida Spodosols.     

Field investigation of high-volume fly ash pavement concrete

Field investigation of high-volume fly ash (HVFA) concrete in pavement construction was carried out. Test results performed on cores drilled from pavement after 270 days of concrete age showed that use of HVFA results in production of pavement concrete with improvements in: strength; moisture barrier qualities; and abrasive resistance characteristics. These improvements are brought about by the pozzolanic reaction of fly ash with the hydrates of cement that favorably changes the microstructure and interfacial transition zone in the resulting concrete.Use of high volume of fly ash in pavement concrete as partial replacement for cement is estimated to produce major energy and environmental gains and is a practice that is aimed at producing durable and sustainable concrete-based infrastructure. The use of HVFA concrete can significantly economize the construction of concrete pavements and improve the service life of transportation infrastructure.     

应用反渗透技术处理垃圾填埋场渗滤液

垃圾填埋场渗滤液属于高浓度氨氮废水，其水量、水质特性变化大，成分复杂，因此较难处理。反渗透分离技术能有效截留垃圾渗滤液中溶解态的有机和无机污染物。采用三级反渗透处理垃圾渗滤液工艺处理后的出水水质，能够满足《生活垃圾填埋污染控制标准》（DB16889-2008）要求，并把渗滤液浓缩液回灌于填埋场。     

Environmental impacts of asphalt mixes with electric arc furnace steel slag

Electric arc furnace (EAF) steel slag can be used as an alternative high-quality material in road construction. Although asphalts with slag aggregates have been recognized as environmentally acceptable, there is a lack of data concerning the potential leaching of toxic Cr(VI) due to the highly alkaline media of EAF slag. Leaching of selected water extractable metals from slag indicated elevated concentrations of total chromium and Cr(VI). To estimate the environmental impacts of asphalt mixes with slag, leachability tests based on diffusion were performed using pure water and salt water as leaching agents. Compact and ground asphalt composites with natural aggregates, and asphalt composites in which the natural aggregates were completely replaced by slag were prepared. The concentrations of total chromium and Cr(VI) were determined in leachates over a time period of 6 mo. After 1 and 6 mo, the concentrations of some other metals were also determined in the leachates. The results indicated that chromium in leachates from asphalt composites with the addition of slag was present almost solely in its hexavalent form. However, the concentrations were very low (below 25 μg L) and did not represent an environmental burden. The leaching of other metals from asphalt composites with the addition of slag was negligible. Therefore, the investigated EAF slag can be considered as environmentally safe substitute for natural aggregates in asphalt mixes.     

Life cycle assessment of hot mix asphalt and zeolite-based warm mix asphalt with reclaimed asphalt pavement

A comprehensive life cycle assessment of asphalt pavements was conducted including hot mix asphalt (HMA), warm mix asphalt (WMA) with the addition of synthetic zeolites, and asphalt mixes with reclaimed asphalt pavement (RAP). The environmental impacts associated with energy consumption and air emissions were assessed, as well as other environmental impacts resulting from the extraction and processing of minerals, binders and chemical additives; asphalt production; transportation of materials; asphalt paving; road traffic on the pavement; land use; dismantling of the pavement at the end-of-life and its landfill disposal or recycling. Monte Carlo simulations were also conducted to take into account the variability of critical input parameters. Taking into account the entire life cycle, the impacts of zeolite-based WMA pavements were almost equal to the impacts of HMA pavements with the same RAP content. The reduction in the impacts of WMA resulting from the lowering of the manufacturing temperature was offset by the greater impacts of the materials used, especially the impacts of the synthetic zeolites. Moreover, by comparing asphalt mixes with different RAP contents, it was shown that the impacts of asphalt mixes were significantly reduced when RAP was added. All endpoint impacts as well as climate change, fossil depletion and total cumulative energy demand were decreased by 13–14% by adding 15% RAP. A key advantage of WMA is the potentially greater use of RAP. Thus, the decrease in the impacts achieved by adding large amounts of RAP to WMA could turn these asphalt mixes into a good alternative to HMA in environmental terms.     

含Cr（Ⅵ）废水生物处理技术及其影响因素

本文综述了微生物还原处理含价铬的废水的研究进展。讨论了影响微生物还原Cr(Ⅵ）因素包括生物体密度、初始Cr（Ⅵ）的浓度、碳源、pH、温度、溶解氧、氧化还原电位、含氧阴离子和金属离子。微生物还原Cr（Ⅵ）技术作为一种富有创新的研究应用于Cr（Ⅵ）污染的环境恢复。     

Runoff water quality from turfgrass established using volume-based composted municipal biosolids applications

Municipal programs for turfgrass establishment recommend large volume-based application rates of composted municipal biosolids (CMB). This study compared runoff water quality among combinations of two common turfgrass establishment practices and two CMB sources. Bryan- or Austin-CMB were incorporated into 5 cm of soil at a rate of 12.5 or 25% by volume (v/v) on an 8.5% slope. Tifway bermudagrass [Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt-Davy, var. Tifway] sprigs were planted and established; sod, produced at a separate site using either CMB amendment at the 25% v/v rate, was transplanted to the runoff plots on the same day. A mature stand of bermudagrass was used as a control. Runoff water was collected after each of eight natural rain events during the sampling period. Total runoff water loss (mm) was similar for the CMB-amended sprigged and transplanted sod stands. The concentration of total dissolved P (TDP) in runoff water was greatest from the transplanted sod in the first seven rain events (4.1 to 7.5 mg L(-1)). The concentration of TDP in runoff water was similar at both the 12.5 and 25% v/v incorporation rates. Regression analysis indicated Mehlich-3-extractable soil test P concentrations in soil amended with CMB were positively correlated to concentration and mass loss of dissolved P in runoff. At similar application rates, dissolved P loss in runoff water was reduced by incorporating CMB into the soil on site rather than transplanting sod produced with CMB.     

Characterization of pollutants in Florida street sweepings for management and reuse

Disposal and beneficial-use options for street sweeping residuals collected as part of routine roadway maintenance activities in Florida, USA, were assessed by characterizing approximately 200 samples collected from 20 municipalities. Total concentrations (mg/kg or μg/kg) and leachable concentrations (mg/L or μg/L) of 11 metals and a number of organic pollutant groups (volatile organics, semi-volatile organics, pesticides, herbicides, carbamates) in the samples were measured. The synthetic precipitation leaching procedure (SPLP) was performed to evaluate the leachability of the pollutants. From the total metal analysis, several metals (e.g., arsenic, barium, chromium, copper, nickel, lead, and zinc) were commonly found above their detection limits. Zinc was found to have the highest mean concentration of all metals measured (46.7 mg/kg), followed by copper (10.7 mg/kg) and barium (10.5 mg/kg). The metal with the smallest mean concentration was arsenic (0.48 mg/kg). A small fraction of the total arsenic, barium, lead, and zinc leached in some samples using the SPLP; leached concentrations were relatively low. A few organic compounds (e.g., 4,4′-DDT, endrin, and endosulfan II) were detected in a limited number of samples. When the total and leaching results were compared to risk-based Florida soil cleanup target levels and groundwater cleanup target levels, the street sweepings were not found to pose a significant human-health risk via direct exposure or groundwater contamination.     

Leaching mechanisms of Cr(VI) from chromite ore processing residue

Batch leaching tests, qualitative and quantitative x-ray powder diffraction (XRPD) analyses, and geochemical modeling were used to investigate the leaching mechanisms of Cr(VI) from chromite ore processing residue (COPR) samples obtained from an urban area in Hudson County, New Jersey. The pH of the leaching solutions was adjusted to cover a wide range between 1 and 12.5. The concentration levels for total chromium (Cr) and Cr(VI) in the leaching solutions were virtually identical for pH values >5. For pH values <5, the concentration of total Cr exceeded that of Cr(VI) with the difference between the two attributed to Cr(III). Geochemical modeling results indicated that the solubility of Cr(VI) is controlled by Cr(VI)-hydrocalumite and Cr(VI)-ettringite at pH >10.5 and by adsorption at pH <8. However, experimental results suggested that Cr(VI) solubility is controlled partially by Cr(VI)-hydrocalumite at pH >10.5 and by hydrotalcites at pH >8 in addition to adsorption of anionic chromate species onto inherently present metal oxides and hydroxides at pH <8. As pH decreased to <10, most of the Cr(VI) bearing minerals become unstable and their dissolution contributes to the increase in Cr(VI) concentration in the leachate solution. At low pH ( <1.5), Cr(III) solid phases and the oxides responsible for Cr(VI) adsorption dissolve and release Cr(III) and Cr(VI) into solution.     

Permeability predictions for sand-clogged Portland cement pervious concrete pavement systems

Pervious concrete is an alternative paving surface that can be used to reduce the nonpoint source pollution effects of stormwater runoff from paved surfaces such as roadways and parking lots by allowing some of the rainfall to permeate into the ground below. This infiltration rate may be adversely affected by clogging of the system, particularly clogging or covering by sand in coastal areas. A theoretical relation was developed between the effective permeability of a sand-clogged pervious concrete block, the permeability of sand, and the porosity of the unclogged block. Permeabilities were then measured for Portland cement pervious concrete systems fully covered with extra fine sand in a flume using simulated rainfalls. The experimental results correlated well with the theoretical calculated permeability of the pervious concrete system for pervious concrete systems fully covered on the surface with sand. Two different slopes (2% and 10%) were used. Rainfall rates were simulated for the combination of direct rainfall (passive runoff) and for additional stormwater runoff from adjacent areas (active runoff). A typical pervious concrete block will allow water to pass through at flow rates greater than 0.2 cm/s and a typical extra fine sand will have a permeability of approximately 0.02 cm/s. The limit of the system with complete sand coverage resulted in an effective system permeability of approximately 0.004 cm/s which is similar to the rainfall intensity of a 30 min duration, 100-year frequency event in the southeastern United States. The results obtained are important in designing and evaluating pervious concrete as a paving surface within watershed management systems for controlling the quantity of runoff.     

Using simulated rainfall to evaluate field and indoor surface runoff phosphorus relationships

While numerous studies have evaluated the efficacy of outdoor rainfall simulations to predict P concentrations in surface runoff, few studies have linked indoor rainfall simulations to P concentrations in surface runoff from agricultural fields. The objective of this study was to evaluate the capacity of indoor rainfall simulation to predict total dissolved P concentrations [TP(<0.45)] in field runoff for four dominant agricultural soils in South Dakota. Surface runoff from 10 residue-free field plots (2 m wide by 2 m long, 2-3% slope) and packed soil boxes (1 m long by 20 cm wide by 7.5 cm high, 2-3% slope) was compared. Surface runoff was generated via rainfall simulation at an intensity of 65 mm h(-1) and was collected for 30 min. Packed boxes produced approximately 24% more runoff (range = 2.8-3.4 cm) than field plots (range = 2.3-2.7 cm) among all soils. No statistical differences in either TP(<0.45) concentration or TP(<0.45) loss was observed in runoff from packed boxes and field plots among soil series (0.17 < P < 0.83). Three of four soils showed significantly more total P lost from packed boxes than field plots. The TP(<0.45) concentration in surface runoff from field plots can be predicted from TP(<0.45) concentration in surface runoff from the packed boxes (0.68 < r(2) < 0.94). A single relationship was derived to predict field TP(<0.45) concentration in surface runoff using surface runoff TP(<0.45) concentration from packed boxes. Evidence is provided that indoor runoff can adequately predict TP(<0.45) concentration in field surface runoff for select soils.