Dosing free nitrous acid for sulfide control in sewers: Results of field trials in Australia

Intermittent dosing of free nitrous acid (FNA), with or without the simultaneous dosing of hydrogen peroxide, is a new strategy developed recently for the control of sulfide production in sewers. Six-month field trials have been carried out in a rising main sewer in Australia (150 mm in diameter and 1080 m in length) to evaluate the performance of the strategy that was previously demonstrated in laboratory studies. In each trial, FNA was dosed at a pumping station for a period of 8 or 24 h, some with simultaneous hydrogen peroxide dosing. The sulfide control effectiveness was monitored by measuring, on-line, the dissolved sulfide concentration at a downstream location of the pipeline (828 m from the pumping station) and the gaseous H₂S concentration at the discharge manhole. Effective sulfide control was achieved in all nine consecutive trials, with sulfide production reduced by more than 80% in 10 days following each dose. Later trials achieved better control efficiency than the first few trials possibly due to the disrupting effects of FNA on sewer biofilms. This suggests that an initial strong dose (more chemical consumption) followed by maintenance dosing (less chemical consumption) could be a very cost-effective way to achieve consistent control efficiency. It was also found that heavy rainfall slowed the recovery of sulfide production after dosing, likely due to the dilution effects and reduced retention time. Overall, intermittent dose of FNA or FNA in combination with H₂O₂ was successfully demonstrated to be a cost-effective method for sulfide control in rising main sewers.     

Bond strength of steel bars embedded in high-performance fiber-reinforced cementitious composite before and after exposure to elevated temperatures

Interfacial bond strengths of steel reinforcing bars embedded in a high-performance fiber-reinforced cementitious composite (HPFRCC) are investigated in this paper. Out of 303 pullout specimens, 48 HPFRCC and 3 normal concrete specimens were tested without any heat treatment, and 240 HPFRCC and 12 normal concrete specimens were heated at 200, 400, 600, or 800 °C in a furnace for 2 h prior to testing. The effects of bar shape, diameter, and length embedded in HPFRCC on the bond strength of HPFRCC specimens were investigated. The bond strength decreased with the heating temperature and with the size and embedded length of steel bars. It was reduced further when the heated specimens were cooled in water instead of air. It was disaggregated into chemical adhesion and mechanical interlock from a comparative study of plain and deformed bars. The mechanical properties and microstructures of HPFRCC specimens before and after heat treatment were compared to understand the mechanisms of interfacial bonding degradation due to heat treatment.     

Analytical frameworks to incorporate demand response in long-term resource planning

Many utilities are obligated by state regulatory or legislative requirements to consider demand response (DR) as part of their resource planning process. There are several ways to incorporate DR into resource planning modeling and each has its advantages and disadvantages. We explore the current analytical frameworks for incorporating DR into long-term resource planning. We also consider whether current approaches accurately and realistically model DR resources in capacity expansion and production cost models and whether barriers exist to incorporating DR into resource planning models in a more robust fashion. We identify 10 specific recommendations for enhancing and expanding the current approaches.     

Customer bill impacts of energy efficiency and net-metered photovoltaic system investments

Utility regulators and policymakers are concerned about potential increases in retail rates driven by energy efficiency (EE) programs and distributed solar photovoltaic (PV) systems, which may adversely affect utility customers that do not invest in these technologies (i.e., non-participants) and more so than those that do (i.e., participants). We assess customer bill impacts of illustrative EE programs and net-metered PV systems for a prototypical northeast utility. We find that the timing of customer EE or PV investments matters and that modest energy savings may fail to yield financial benefits sufficient to offset concomitant increases in retail rates.     

The electricity balancing market: Exploring the design challenge

In the unbundled national electricity markets in Europe, the balancing market is the institutional arrangement that deals with the balancing of electricity demand and supply. This paper presents a framework for policy makers that identifies the relevant design variables and performance criteria that play a role in the design and analysis of European balancing markets. We outline the full extent of the design challenge through a discussion of trade-offs among performance criteria, uncertain effects of design variables, and the many inter-linkages between the balancing market and the electricity market at large. Policy makers can address the balancing market design challenge by adopting a structured approach in which design variables, performance criteria, market conditions, system developments, and resultant market incentives are explicitly considered.     

Efficiency of urban water supply in Sub-Saharan Africa: Do organization and regulation matter?

Using the model developed by Battese and Coelli (1995), we compare the technical efficiency of urban water utilities in Sub-Saharan Africa countries. We examine how private-sector participation, economic regulation, and their combination affects technical efficiency. We find that regulating water utility operations via performance contracts leads to higher technical efficiency compared to control by an independent regulatory agency. Private-sector participation in management has a positive effect on technical efficiency. However, there is no evidence of a statistically significant difference between the technical efficiency of publicly and privately owned utilities, respectively, when they are regulated by either an independent agency or a performance contract.     

A study of the negotiated-settlement practice in regulation: Some evidence from Florida

Negotiated settlements have become a frequently used alternative to contested proceedings when setting prices charged by public utilities under the US rate-of-return regulatory model. The behavior of the representatives of consumer advocates and the firms during settlement negotiations determine customer prices. This paper examines this behavior by using data from the Florida Public Service Commission to estimate the payoff functions of both parties. The estimation suggests that the advocate and the firm weight the present rate change more than the consumer's future average price and the firm's future operating revenue in their settlement decisions. It also indicates that the time saved by settlements is not a primary reason for their popularity.     

Investigation of mixing ratio and restraint condition effects on alkali–silica gel pressure in mortar by using a uniaxial alkali–silica gel pressure measuring device (ASGPM-D)

A pressure of alkali silica gel which is the product of alkali–silica reaction causes pattern crack development and ultimately failure in cement based materials. This paper examines the measurement of alkali–silica gel pressure in cylindrical mortar specimen by a new test device (alkali–silica gel pressure measuring device, ASGPM-D) and investigates also the effects of the test medium on test results. Specimens of various sizes and geometries were tested to develop standard specimen size for ASGPM test method. The most suitable specimen with diameter of 35 mm and 250 mm in length was selected by optimizing the experimental results. Furthermore, the highest alkali–silica pressure value was recorded on a specimen which has 0.45 w/c and 74–150 μm grain size in an 80 °C 1 N NaOH solution. Also, swelling pressures of four reactive aggregates (opal, chert, basalt and chalcedony) were determined under two distinct restraint stages (1.5 kN and 3 kN).     

Experimental behaviour of cold-formed steel welded tube filled with concrete made of crushed crystallized slag subjected to eccentric load

This paper presents results of tests conducted on thin welded rectangular steel stubs filled with concrete that gravel was substituted by 10 mm crushed crystallized slag stone. The studied section was made of two cold steel plates with U shape and welded with electric arc to form a steel box section. The cross-section dimensions were: 100×70×2 mm³. the main studied parameters were the stub height (200, 300, 400, 500 mm), the effect of the in filled concrete, the continued weld and the eccentric force. The tests were carried out 28 days after the date of casting. A total of 20 stubs were tested in a 50 tf machine up to failure, 4 stubs subjected to axial load compression and 16 stubs subjected to eccentric load compression along the minor and major rigidity axis. The aim of the study is to provide some evidences that the use of crushed slag could be integrated in the manufacturing of non-conventional concrete. All failure loads were predicted by using the Euro code 4 and the design method proposed by Z. Vrcelj and B. Uy. From test results, it was confirmed that the length of stubs and the eccentric load had a drastic effect on the load carrying capacity. The failure mode of composite stubs was a local buckling mode with all steel sides deformed outwards. The Euro code 4 loads predictions were generally in good agreement compared with experimental loads and on safe side. The loads results of design method proposed by Vrcelj and B. Uy were generally on safe side compared with experimental load except the columns subject to eccentric load with 400 mm and 500 mm height.     

Slate flexural and anchorage strength considerations in cladding design

This paper describes an experimental investigation on the flexural and anchorage strength of slate for cladding. The study has been conducted on sawed slate specimens, all showing the same surface finishing. Slate flexural strength was compared for two distinct situations: (i) using a 3-Point flexure loading configuration in batches of materials with larger cross-sectional specimen dimension (50 × 30 mm²); and (ii) using a 4-Point flexure loading configuration in the same batch of materials but with smaller cross-sectional dimensions (30 × 25 mm²). The 4-Point bending specimens were tested in three different directions considering slate anisotropy planes. Load was applied along the direction perpendicular to the planes of schistosity; and also along two directions parallel to the planes of schistosity. Slate anchorage strength has been determined on slate slabs with 400 × 200 × 30 mm³ with dowel anchorage in 8 mm diameter cylindrical holes with 35 mm depth. Test load was applied perpendicularly to the schistosity planes. Cladding stone in building facades and its supporting systems must be compatible with the behaviour and performance of other interfacing systems, such as curtain walls and superstructure frames. In this sense, a properly executed dimensional stone cladding should be designed and installed within the capabilities and limitations of the slate’s support system to resist all active forces or actions. The results of this work reveal the importance of complementary characterization techniques for dimension stone cladding, particularly for anisotropic rocks as slates. From the results it is possible to conclude that schistosity planes have an utter influence on either anchorage or flexural strength.     

Modelling the cleaning performance of rotating brush in duct cleaning

The bristle of a rotating duct cleaning brush was modelled using large deformation elastic theory. In addition to contact and centrifugal forces, especially the effect of air drag was studied in the article. The dependence of the drag coefficient on air speed was simulated for numerical computations by fitting a fourth degree polynomial in logarithmic co-ordinates on point-wise data for a cylindrical body from literature.The results show that the effect of air drag on the deflection of the single bristle (L=1 mm, d=1 mm, ρ_b=1140 m³/kg, EI=2 GPa) is negligible at normal rotating speeds of the brush (300−1000 rpm). However, air drag may affect considerably the deflection of a bristle, which has a large diameter and low density. As to be expected, air drag decreases the contact force between the single bristle tip and duct surface even at low rotation speed of bristle (<50 rpm). Thicker or stiffer bristle decreases the deflection of the rotating bristle and increases the magnitude of the contact normal force between the bristle tip and the duct surface. The model presented combined with the Mathcad software seems to be a useful tool in the cleaning brush design work.     

Down-Hole Triaxial Test to Measure Average Stress-Strain Relationship of Rock Mass

A new field test method was proposed for the purpose of measuring average stress-strain relationships of rock masses. The test is conducted on a hollow cylindrical specimen prepared at the bottom of a drill-hole. Average axial as well as lateral strains can be measured in a center hole and an outer slit by a noel technique of instrumentation for cavity deformation.A set of test equipment for this test method was developed at Central Research Institute of Electric Power Industry, CRIEPI, in Japan for prototype tests. Specimens of 400 mm in outer diameter and 1050 mm in height can be sheared under confining pressures as high as 5.0 MPa. Accuracy of strain measurements was designed to be of the order of 10^-4.Trial series of tests were carried out at the site of rhyolitic tuffacious rock formation. The results, similar to conventional laboratory triaxial tests, proved that the proposed test method was successful to measure average stress-strain relationships of large rock specimens. Considering the significant size of the specimens, the volume of rock involved in the tests is of the same order or greater than those in conventional field rock tests, such as plate load tests and rock shear tests. As a consequence, the test results are considered as representative in evaluation of strength and deformation characteristics of rock masses but not rock cores.     

Rheology of fire-fighting foams

This paper examines the rheological properties of compressed-air foams and contains velocity profiles of foams flowing through straight horizontal tubes. It is shown that a master equation can be derived from the experimental data to account for a range of expansion ratios and pressures normally encountered during pumping of polyhedral-in-structure fire-fighting foams. The experimental data come from a Poiseuille-flow rheometer consisting of three stainless steel tubes 6.95, 9.9, 15.8 mm in diameter, with foam generated by mixing a pressurised solution of Class A foam with compressed air. Results are corrected for wall slip following the method of Oldroyd-Jastrzebski, which implies the dependence of slip coefficients on the curvature of the tube wall. The experimental results demonstrate the applicability of the volume equalisation method to the more expanded, polyhedral (ε>5) and transition, bubbly-to-polyhedral (5⩾ε⩾4) foams. (The method of volume equalisation was introduced by Valkó and Economides to correlate the viscosity of low expansion foams (ε<4), characterised by spherical bubbles.) The present results indicate that all data points align themselves along two master curves, depending on whether the foam consists of bubbles or polyhedral cells.     

Investigation on square concrete filled double-skin steel tube (CFDST) subjected to local bearing force: Experiments

Experimental studies on the behaviour of concrete filled double-skin steel tube (CFDST) subjected to local bearing forces are presented in this paper. Sixteen specimens were prepared and tested with the included angle between bearing member (BM) and compression member of 45° and 90°, whilst both the inner and outer steel tubes of the CFDST specimens are square hollow sections (SHS). The main parameters in the tests were: 1) outside width ratio between BM and compression member: from 0.4 to 0.6; 2) hollow ratio of CFDST: from 0 to 0.6; 3) wall thickness of outer steel tube: 3.05 mm and 3.95 mm; and 4) cross-section of BM: solid and hollow. The failure pattern, load versus deformation curve, bearing capacity and corresponding deformation at bearing capacity of the tested specimens are presented and analyzed. The experimental results show that, while subjected to local bearing forces, CFDST specimens have a high bearing capacity and a good deformation-resistant ability. The calculated bearing capacities of CFDST under local bearing forces using the proposed formulae in the paper are evaluated by comparison with the experimental results.     

Structural behavior and performance of water pipes rehabilitated with a fast-setting polyurea–urethane lining

This paper presents the structural behavior and performance of a fast-setting polyurea–urethane (PUU) lining as a structural lining material for rehabilitating water pipes. To this end, a series of experimental tests were carried out to assess the following: (1) bond strength; (2) hole and gap spanning capabilities; (3) angular displacement ability; (4) transverse shear resistance; and (5) fatigue cyclic loading resistance. First, pull-off bond tests were conducted to evaluate the bond characteristics of a fast-setting PUU lining bonded to steel specimens. Surfaces were dried to ensure adequate bond strength. Second, hole and gap spanning tests were carried out to investigate the spanning capability of the lining on the water pipes. From these tests, the hole spanning capability of water pipe with 5 mm hole was observed to be 11 MPa. Then, angular displacement and transverse shear tests on fast-setting PUU lined water pipes were also carried out to evaluate the behavior and performance in bending and shear of this material. Peel off failure of PUU occurred at an angular displacement capacity of 6.74° and no failure of PUU was observed at a transverse shear capacity of 25% of the diameter. Finally, fatigue cyclic loading test was conducted to investigate the fatigue behavior and performance of the water pipe lined with this PUU material. The fatigue resistance of PUU in the range of 10⁵ cyclic loadings was achieved.     

Structural behavior of concrete filled steel tubular sections (CFT/CFSt) under axial compression

In this study, compressive strength, modulus of elasticity and steel tensile coupon tests are performed to determine material properties. Sixteen hollow cold formed steel tubes and 48 concrete filled steel tube specimens are used for axial compression tests. The effects of width/thickness ratio (b/t), the compressive strength of concrete and geometrical shape of cross section parameters on ultimate loads, axial stress, ductility and buckling behavior are investigated. Circular, hexagonal, rectangular and square sections, 18.75, 30.00, 50.00, 100.00 b/t ratio values and 13, 26, 35 MPa concrete compressive strength values are chosen for the experimental procedure. Analytical models of specimens are developed using a finite element program (ABAQUS) and the results are compared. Circular specimens are the most effective samples according to both axial stress and ductility values. The concrete in tubes has experienced considerable amount of deformations which is not expected from such a brittle material in certain cases. The results provide an innovative perspective on using cold formed steel and concrete together as a composite material.     

Characterization of aerosols emissions from the combustion of dead shrub twigs and leaves using a cone calorimeter

This work is a contribution to the understanding of wildfire smoke emissions. It focuses on the characterization of aerosols emitted by the combustion of dead shrub leaves and twigs with different thickness (range of 0.75–20 mm). The experiments were carried out at bench scale with a cone calorimeter for the burning of Cistus monspeliensis leaves and twigs. Auto-ignition of the samples was obtained by heating their surface with a radiant heat flux of 50 kW/m². The smoke and aerosols emitted before ignition during pre-heating were analysed separately from the smoke and aerosols emitted during the flaming phase. Heat release rate (HRR) was also measured and we observed two different behaviours depending on the diameter of the twigs. Fuel samples with diameter smaller than 4 mm exhibit a single peak HRR whereas two peaks were observed for the twigs with larger diameters. The smoke production rate (SPR) was also measured and it showed that smoke was mainly emitted during the pre-heating phase. We also obtained a strong correlation between HRR and SPR during the flaming phase but no smoke was emitted during the glowing phase. Emission factors of aerosols were calculated depending on these combustion phases (pre-ignition and flaming) and for the range of thickness of the samples. The observations of the aerosols were performed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The chemical composition of organic carbon (OC) aerosols, emitted during the pre-ignition phase, were analysed using gas chromatography (GC) coupled with mass spectrometry (MS). Some carcinogenic compounds were identified. The sizes of OC and black carbon (BC) aerosols emitted were measured with an optical device. Most of the BC were PM_0.3, which corresponds to the alveolar fraction of particles.     

Flame spread over horizontal and vertical wires: The role of dripping and core

Dripping of polymer insulations in wire fire has a potential risk of igniting nearby objects and expanding the size of fire, but has not been well studied so far. In this experimental study, dripping behaviors during the flame spread over horizontal and vertical polyethylene (PE) insulated wires were investigated without external airflow. Two different wire dimensions – core/wire diameter of 3.5/8.0 and 5.5/9.0 mm – and three different PE insulations were tested. To identify effects of the core, wires with solid copper (Cu) core, hollow stainless steel (SS) core, and without core were tested, and both core and insulation temperatures were also measured during the flame spread. Experimental results showed that the high-conductance copper core acted as a heat source downstream to increase the flame-spread rate. However, in the upstream burning zone, the copper core also acted as a heat sink to cool the molten insulation and reduce its mobility. Thus, the copper core extended the residence time of molten insulation inside the flame to facilitate the burning while reducing the dripping. Moreover, for the downward flame spread, the heating by the dripping flow of hot molten insulation dominated over the heating by the core. The downward dripping flow is driven by gravity while limited by the viscous and surface tension forces. Therefore, the limited dripping flow along the cooler copper core reduced the downward flame spread. The trend of results was also found to be insensitive to the type of PE insulation. This is the first time that within a single flame, the simultaneous dual effect of the heat source and heat sink for the wire core was observed, and the influence of dripping on the flame spread over the wire was discovered.