摘要:

Pilot-scale research was conducted to quantify the effects of stabilizing combined wastewater sludges (primary and biological nutrient removal waste activated sludges), in a common high-rate, single-stage anaerobic digestion operation. Various ratios of primary to waste activated sludge were used, and digester operational efficiency was assessed on the basis of the amount and rate of volatile mass removal, biogas production, and digester supernatant quality. It was found that, depending on the sludge ratio, addition of the biological nutrient removal waste activated sludge decreased digester operational efficiency; for example, almost 20% less volatile mass reduction, up to 25% reduction in metabolic reaction rates, and reduced gas production rates of up to 40% were observed. This was attributed to the presence of the cell membrane encapsulating the fermentable substrates of waste activated sludge, making them less available in the digestion process. It was concluded that, unless some type of pretreatment operation is utilized to liberate these substrates, this type of commonly used codigestion system will be of less benefit to a wastewater treatment plant, especially the smaller facilities which will lose a ready source of power in the form of biogas production, and the full value of the waste activated sludge as a resource will not be realized.Key words: anaerobic sludge digestion, biogas production, biological nutrient removal, biosolids, combined sludge, fermentation, volatile mass reduction.

ISSN:0315-1468    

DOI:10.1139/l95-032

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Five hydrologically based instream flow assessment methods are compared for 70 rivers in Atlantic Canada; these methods included (i) Tennant method; (ii) 25% mean annual flow (25% MAF); (iii) median monthly flow (Q50) which includes the aquatic base flow (ABF); (iv) the flow equalled or exceeded 90% of time on a monthly flow duration curve (Q90); and (v) the statistical 7-day low flow frequency of a 10-year recurrence interval (7Q10). By comparing the different methods relative to the 25% MAF (the commonly used method in Atlantic Canada), we found that theQ90and 7Q10 methods predicted extremely low instream flows during winter and summer months. Resource management decisions based on these extremely low flow predictions could have serious adverse consequences. The median monthly flow method (Q50) was recommended for gauged basins, whereas the Tennant method, the 25% MAF method, and the ABF methods were recommended for ungauged basins. For ungauged basins, we conducted a regional study to estimate the 25% MAF and the ABF using multiple regression analysis. Physiographic parameters were used as explanatory variables in the regression analysis. Based on the coefficient of determination,R2, the best regression results were obtained for the 25% MAF withR2ranging from 0.957 to 0.999. Although the results for ABF were slightly lower than for the 25% MAF,R2was still in the range of 0.868 to 0.979.Key words: environmental assessment, maintenance flow, low flow, aquatic resources.

ISSN:0315-1468    

DOI:10.1139/l95-033

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Recently, spillways with a stepped profile have regained interest and favor among design engineers to pass flood waters over the dams. The stepped geometry enhances the energy dissipation above the spillway and reduces the size of a downstream stilling basin. In this paper, the author shows that the technique of stepped channels has been developed since Antiquity. Spillways and irrigation channels with stepped profiles were developed by several civilisations around the Mediterranean sea and in America. The main characteristics of the stepped spillways along the ages suggest a regular evolution rather than a revolution. Present stepped spillways are designed to pass similar discharges as 200 years ago.Key words: stepped channels, spillway, irrigation system, history, design techniques, energy dissipation.

ISSN:0315-1468    

DOI:10.1139/l95-034

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

This research discusses two strategies for adding acetate to sequencing batch reactors operating as biological removal (Bio-P) systems. The control (fixed-time) reactor adds the acetate at a set time of 1 h 25 min, which is anassumedtime for complete denitrification. The experimental (real-time) reactor adds the acetate when a computer detects the disappearance of nitrates, as indicated by a distinctive "breakpoint" or "kink" in the oxidation-reduction potential versus time profile. This control strategy is therefore based upon aknowntime for complete denitrification. The time-of-occurrence of the nitrate breakpoint is utilized in the development of a screening protocol for interpreting the behaviour (in terms of nitrate reactions) for reactors operating in biological phosphorus removal mode. The protocol involves categorizing the timing of the nitrate breakpoint into two groupings. A "failure" category corresponds to acetate being added prior to the breakpoint, because, in these cases, the acetate is used partially for denitrification and partially for Bio-P carbon storage. A "success" category corresponds to breakpoints occurring prior to the addition of acetate. In such cases, acetate is used solely for carbon storage by Bio-P organisms.Key words: oxidation-reduction potential, biological phosphorus removal, sequencing batch reactor, real-time computer control.

ISSN:0315-1468    

DOI:10.1139/l95-035

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The response of a small lake or reservoir system to wind and streamflow forcing is examined in this paper using a numerical model based on Navier–Stokes equation and a numerical hydraulic model using the segment-node approach. The main mass transport in the lake has been found to be due to wind; the circulation caused by stream inflow and outflow of the lake contributes a relatively small fraction of the total transport. The above-mentioned models have been applied to different wind regimes and constant or variable inflow–outflow conditions of Long Lake (Nova Scotia). Comparisons are made between observed data and model results by both models. The model response has also been studied for generation of seiches and wind setup in the lake; and the response of the lake to these forcing functions has been presented. The comparison of model results within situfield data establishes model's suitability to make predictions. Drogue and water level measurements were made at a number of locations in the Long Lake to validate the numerical models. The results from the numerical simulation using the two models compare favourably with the observed data. As may be expected, the segment-node modelling scheme was found to be computationally more efficient and relatively easy to run on a personal computer.Key words: numerical model, hydrodynamics, circulation, Long Lake, temperature, dissolved oxygen, stratification, Nova Scotia.

ISSN:0315-1468    

DOI:10.1139/l95-036

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Over the last 15 years, extensive research has been done on the transferability of travel demand models. However, much of this work has been concentrated towards investigating the transferability of disaggregate mode choice models. The transferability of an aggregate total demand model for intercity travel is examined. Model transfer is possible only when a number of preconditions for transferability are satisfied. One of the principal obstacles to the successful transfer of intercity demand models is the inability to overcome the contextual differences between calibration and application. Here, the components of the intercity total demand model are separated into exogenous and intrinsic (contextual) factors. The latter is thereafter classified as being either transferable or nontransferable. It is shown that transferable attributes can accompany a model during transfer. Nontransferable attributes, on the other hand, will free the model of city or city-pair specific contextual characteristics which should not be transferred to other city pairs. The issues involved in transferring an aggregate model are also investigated. Aggregate data on interdistrict travel by public transportation in Sri Lanka have been used to successfully calibrate a total demand model with a number of transferable and nontransferable attributes that represent both temporal and spatial contextual factors. It is shown that the forecasting ability of this model is far superior to a counterpart model without the intrinsic variables.Key words: travel demand, aggregate, forecasting, transferability, intercity, Sri Lanka.

ISSN:0315-1468    

DOI:10.1139/l95-037

出版商:NRC Research Press    

年代:1995

数据来源: NRC

ISSN:0315-1468    

DOI:10.1139/l95-038

出版商:NRC Research Press    

年代:1995

数据来源: NRC

ISSN:0315-1468    

DOI:10.1139/l95-039

出版商:NRC Research Press    

年代:1995

数据来源: NRC

ISSN:0315-1468    

DOI:10.1139/l95-041

出版商:NRC Research Press    

年代:1995

数据来源: NRC

ISSN:0315-1468    

DOI:10.1139/l95-042

出版商:NRC Research Press    

年代:1995

数据来源: NRC