Investigations of hydraulic operating conditions of air lift pump with three types of air-water mixers. The paper presents the analysis of results of the investigations concerning the influence of various constructive solutions of the air-water mixers on hydraulic operating conditions of the air lift pump. The scope of the investigations encompassed the determination of characteristics of delivery head and delivery rate for three types of air-water mixers applied in the constructed air lift pump. Using the obtained results, the efficiency of the three types of air-water mixers applied in this air lift pump was determined. The analysis was carried out and there was checked whether the improved analytical Stenning-Martin model can be used to design air lift pumps with the air-water mixers of these types. The highest capacity in the water transport was reached by the air lift pump with the 1st type air-water mixer, the lowest one – with the 3rd type air-water mixer. The water flow in the air lift pump increases along with the rise in the air flow. The lower are the hydraulic losses generated during flow of the air flux by the air-water mixer, the higher is the air lift pump capacity. Along with the rise in the water delivery head, the capacity of the air lift pump decreases. The highest efficiency is reached by the air lift pump with the 1st type air-water mixer, the lowest – with the 3st type air-water mixer. The efficiency of the air lift pump for the three investigated types of air-water mixers decreases along with the rise in air flow rate and water delivery head. The values of submergence ratio (h/L) of the delivery pipe, calculated with the use of the improved analytical Stenning-Martin model, coincide quite well with the values of h/L determined from the measurements.

The article presents the results of tests of minor head losses through PVC and PP elbows for a flow of water and mixtures of water and sand with grain sizes of up to 0.5 mm and concentrations of 5.6 g·L−1, 10.84 g·L−1, and 15.73 g·L−1. The tests were carried out at variable flow velocities for three elbow diameters of 63 mm, 75 mm, and 90 mm. The flow rate, pressure difference in the tested cross-sections, and temperature of the fluids were measured and automatically recorded. The results of the measurements were used to develop mathematical models for determining the minor head loss coefficient as a function of elbow diameter, sand concentration in the liquid, and Reynolds number. The mathematical model was developed by cross validation. It was shown that when the concentration of sand in the liquid was increased by 1.0 g∙L−1, the coefficient of minor head loss through the elbows increased, in the Reynolds number range of 4.6 × 104–2.1 × 105, by 0.3–0.01% for PP63, 0.6–0.03% for PP75, 1.1–0.06% for PP90, 0.8−0.01% for PVC63, 0.8–0.02% for PVC75, and 0.9–0.04% for PVC90. An increase in Re from 5 × 104 to 2 × 106 for elbows with diameters of 63, 75 and 90 mm caused a 7.3%, 6.8%, and 6.0% decrease in the minor head loss coefficient, respectively.

Abstract:The paper presents the analysis of results of empirical investigations of a negative pressure difference in vacuum pipelines with internal diameters of 57, 81, 102 mm. The investigations were performed in an experimental installation of a vacuum sewage system, built in a laboratory hall on a scale of 1:1. The paper contains a review of the literature concerning two-phase flows (liquid-gas) in horizontal, vertical and diagonal pipelines. It presents the construction and working principles of the experimental installation of vacuum sewage system in steady and unsteady conditions during a two-phase flow of water and air. It also presents a methodology for determination of formula for calculation of a negative pressure difference in vacuum pipelines. The results obtained from the measurements of the negative pressure difference Δpvr in the vacuum pipelines were analyzed and compared with the results of calculations of the negative pressure difference Δpvr, obtained from the determined formula. The values of the negative pressure difference Δpvr calculated for the vacuum pipelines with internal diameters of 57, 81, and 102 mm with the use of Formula (19) coincide with the values of Δpvr measured in the experimental installation of a vacuum sewage system. The dependence of the negative pressure difference Δpvr along the length of the vacuum pipelines on the set negative pressure in the vacuum container pvzp is linear. The smaller the vacuum pipeline diameter, the greater the negative pressure difference Δpvr is along its length.

Model investigations of wastewater purification were carried out in a medium sand bed with an assisting natural clinoptilolite layer 0.10 or 0.25 m thick. The effectiveness of wastewater purification related to basic qualitative parameters was in accordance with the Polish standards on sewage disposal into grounds and surface water. Medium sand soil bed with the assisting natural clinoptilolite layer 0.25 m thick showed on average the removal efficiency regarding TSS higher by 3.3%, total nitrogen by 29.3%, total phosphorus by 25.9%, reduction efficiency regarding BOD5 by 1.1% and COD by 15.9% than that with the thinner clinoptilolite layer. The investigations confirmed that natural clinoptilolite with the granulation 1-5 mm can be used to enhance the removal of nitrogen and phosphorus compounds from wastewater with the application of infiltration drainage. However, very good effect of the TSS removal from the wastewater in the investigated soil beds can lead to their fast clogging under the infiltration drainage. Septic tanks should be designed in such a way that they retain as much TSS as possible, e.g., multi-chamber tanks instead of one-chamber ones.

The model investigations of sewage purification were carried out in a medium sand bed with an assisting hydro-anthracite layer with thickness of 0.10 and 0.20 m. It has been observed that the effectiveness of sewage purification related to basic qualitative parameters (total suspended solids – TSS, BOD5, COD, total nitrogen, total phosphorus) is in accordance with the Polish standards on sewage disposal into grounds and surface water. It has been stated that the medium sand soil bed with the 0.20-meter thick assisting hydro-anthracite layer shows higher effectiveness of sewage purification than the 0.10 m thick assisting layer. This application in the medium sand soil bed increased the removal efficiency regarding TSS by 3.1%, total nitrogen by 29.4%, ammonia nitrogen by 1.2% and total phosphorus by 23.0%, and reduction efficiency regarding BOD5 by 1.5% and COD by 11.3% with relation to the 0.10-meter thick assisting hydro-anthracite layer (all percentages – in average). The investigations confirm that the hydro-anthracite with the granulation of 1.8–2.5 mm can be used to assist in removal of nitrogen and phosphorus compounds from sewages