Strength of ferric hydroxide flocs

Strength and break-up of flocs produced in flocculation of water and effluent with ferric chloride were studied. Floc size was determined by a photographing technique and area and perimeter measurements by a Quantimet apparatus.The experimental results obeyed the expression d_max = GC⁻²γ with γ = 0.3 for effluent and γ = 0.5 for water indicating both viscous and inertial effects in break-up. Floc strength parameter C increased with polymeric coagulant aid addition, higher C values were obtained in water than in effluent.Floc break-up seems to take place by erosion of particles and flocs once disrupted do not grow again.     

Optimalization of coagulant dose in coagulation-flocculation of sewage

This article describes how the optimal coagulant dose in chemical treatment can be calculated from a limited number of raw sewage characteristics. Ferric chloride and aluminium sulphate were used as coagulants. In jar tests ten characteristics were determined in the sewage and for each separate sample of wastewater “optimal” coagulant doses were determined. There was a very high correlation between the “optimal” coagulant dose of aluminium sulphate and ferric chloride and one or two quality parameters of the influent. A comparison was made between aluminium sulphate and ferric chloride as coagulant. The findings were verified in two pilot plants. In one a constant coagulant dose m⁻³ influent was set; in the other plant the coagulant dose was also related to the orthophosphate content of the sewage. By this means a reduction of the coagulant dose was obtained of 35%, while on average the removal percentage of TOC was the same.     

Physico-chemical treatment of municipal wastewater. Coagulation-flocculation

This article traces the possibilities of physico-chemical treatment of domestic sewage with particular attention to coagulation-flocculation processes. As coagulants the following have been used: ferric chloride, hydrated lime and alum. Different types of coagulant aids have been used too. Besides pilot-plant experiments, a large number of batch experiments has been carried out in order to determine the range of optimal doses of coagulants/coagulant aids/pH and so on. The fate of specific organic and inorganic components (proteins, detergents, low organic acids, phosphorus, nitrogen) as well as TOC, BOD and COD in this chemical treatment have been studied. The suspended and most of the colloidal fractions have efficiently been removed. A considerable fraction, which is defined as soluble, has been removed too. The significance of the findings for wastewater treatment processes have been discussed.     

The Capture Effect in FM Receivers

In this paper a theoretical explanation of the capture effect is given by calculating the instantaneous frequency of the output signal of a limiter when two frequency modulated (FM) signals are present at the limiter input. When this signal is applied to a demodulator with unlimited bandwidth, the output signal of the demodulator proves to have an extreme capture effect. When however the demodulator bandwidth is limited, the capture effect is shown not be be extreme. This phenomenon is explained and possibilities are given to minimize the capture effect. Some of the results of measurements on limiters and demodulators are given in this paper; they prove that a weak capture effect can be obtained. A method of calculating the degree of capturing is included.     

Effect of magnesium and calcium precipitation on coagulation-flocculation with lime

Coagulation-flocculation studies were carried out to identify and quantify the organic matter (TOC) fraction removed by Mg (OH)₂ precipitation and the fraction removed due to CaCO₃ precipitation in lime treatment of wastewater. Most experiments were carried out with domestic sewage and some with a tannic acid solution simulating coagulable organics in wastewater. The experiments showed a clear relation between the amount of TOC removed and the amount of Mg (OH)₂ formed. This relation between TOC removal and Mg(OH)₂ precipitation can be expressed in terms of an adsorption isotherm. The coagulation-flocculation tests of sewage with lime as a coagulant indicated that about 26% of the removable TOC in sewage is eliminated by Mg(OH)₂.     

Some dimensionless parameters of impeller power in coagulation-flocculation processes

The simplified equation for impeller power dissipation is well known and power coefficients have been published for most impellers.Most published data apply to cylindrical tanks with or without baffles.This paper is a study of the effect of some impeller and vessel geometry on impeller power dissipation, especially focused on square tanks as commonly used in coagulation-flocculation processes of (waste) waters.The experiments showed that the dimensionless Power number for a square tank can be estimated quite well by the Power number of a baffled cylindrical tank with certain dimensions.The removal of colloidal compounds at a given G value differs with the type of stirrer and vessel applied. The optimal G value is the same for all vessel-stirrer combinations.