Physical–chemical treatment of water and wastewater / Arcadio Pacquiao Sincero, Sr.,. Gregoria Alivio Sincero. p. cm. Includes bibliographical. The books currently available on this subject contain some elements of physical- chemical treatment of water and wastewater but fall short of giving. PDF | Waste-water treatment is becoming even more important in the light of diminishing water resources, increasing industrial, domestic and.
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Physical-Chemical Treatment of Water and Wastewater DownloadPDF MB Read online. The books currently available on this subject. Views 16MB Size Report. DOWNLOAD PDF Physical- chemical treatment of water and wastewater. Read more. patents on treatment of water and wastewater approved during the period from to .. mary treatment processes which include physical-chemical.
Although completely-mixed reactor theory with the assumption of first-order kinetics for BOD removal can be adopted for facultative pond design Marais and Shaw, , such a fundamental approach is rarely adopted in practice.
Instead, an empirical procedure based on operational experience is more common. The most widely adopted design method currently being applied wherever local experience is limited is that introduced by McGarry and Pescod Retention time in a properly designed facultative pond will normally be days and, with a depth of about 1.
On discharge to a surface water, this effluent will not cause problems downstream if the dilution is of the order of and any live algae in the effluent might well be beneficial as a result of photo synthetic oxygen production during daylight hours. Efficiently operating facultative ponds treating wastewater will contain a mixed population of flora but flagellate algal genera such as Chlamydomonas, Euglena, Phacus and Pyrobotrys will predominate.
Non-motile forms such as Chlorella, Scenedesmus and various diatom species will be present in low concentrations unless the pond is underloaded. Algal stratification often occurs in facultative ponds, particularly in the absence of wind-induced mixing, as motile forms respond to changes in light intensity and move in a band up and down the water column. The relative numbers of different genera and their dominance in a facultative pond vary from season to season throughout the year but species diversity generally decreases with increase in loading.
Sometimes, mobile purple sulphur bacteria appear when facultative ponds are overloaded and sulphide concentration increases, with the danger of odour production.
High ammonia concentrations also bring on the same problem and are toxic to algae, especially above pH 8. Maintenance of properly designed facultative ponds will be limited to the removal of scum mats, which tend to accumulate in downwind corners, and the cutting of grass on embankments. To ensure efficient operation, facultative ponds should be regularly monitored but, even where this is not possible, they have the reputation of being relatively trouble-free.
A more important function of maturation ponds, however, is the removal of excreted pathogens to achieve an effluent quality which is suitable for its downstream reuse. Although the longer retention in anaerobic and facultative pond systems will make them more efficient than conventional wastewater treatment processes in removing pathogens, the effluent from a facultative pond treating municipal sewage will generally require further treatment in maturation ponds to reach effluent standards imposed for reuse in unrestricted irrigation.
Faecal coliform bacteria are commonly used as indicators of excreted pathogens and maturation ponds can be designed to achieve a given reduction of faecal coliforms FC. Protozoan cysts and helminth ova are removed by sedimentation in stabilization ponds and a series of ponds with overall retention of 20 days or more will produce an effluent totally free of cysts and ova Feachem et al.
The value of Ne should be obtained by substituting the appropriate levels of variables in Eq 10 assuming a retention time of 7 days in each of two maturation lagoons for sewage.
If the calculated value of Ne does not meet the reuse effluent standard, the number of maturation ponds should be increased, say to three or more each with retention time 5 days, and Ne recalculated. A more systematic approach is now available whereby the optimum design for maturation ponds can be obtained using a simple computer programme Gambrill et al.
Polprasert et al. A multiple-regression equation involving parameters such as retention time, organic loading, algal concentration and ultra-violet light exposure has been suggested. The Wehner and Wilhelm non-ideal flow equation, including the pond dispersion number, was adopted to predict bacterial survival, in preference to the first order rate equation Eq 9 and Maturation ponds will be aerobic throughout the water column during daylight hours and the pH will rise above 9.
The algal population of many species of non-flagellate unicellular and colonial forms will be distributed over the full depth of a maturation pond.
Large numbers of filamentous algae, particularly blue-greens, will emerge under very low BOD loading conditions. Very low concentrations of algae in a maturation pond will indicate excessive algal predation by zooplankton, such as Daphnia sp, and this will have a deleterious effect on pathogen die-off, which is linked to algal activity. Saqqar , in his analysis of the performance of the Al Samra stabilization ponds in Amman, Jordan, has shown that the coliform and faecal coliform die-off coefficients varied with retention time, water temperature, organic loading, total BOD5 concentration, pH and pond depth.
Total coliform die-off was less than the rate of faecal coliform die-off, except during the cold season. This method can also be used for anaerobically stabilised digested and thereafter dewatered sludge. Mixing with bedding materials, such as dry sawdust, may assist in achieving the required solids content as well as attaining the required carbon to nitrogen ratio for composting.
Composting technologies available in the Baltic Sea Region range from simple open windrow systems with a small effort in terms of process structures to fully enclosed composting plants with accelerated treatment processes, complete enclosure and a high quality treatment of exhaust air.
The various technologies are largely proven and well understood in their capabilities and limitations. The most feasible for sludge handling are windrow composting and tunnel composting technologies. The operation and maintenance of both methods are relatively simple and only require a basic understanding of the biology and biochemistry of composting. Summary of hygienisation methods Overview of different hygienisation methods.
Depending on regulations and costs energy, personnel, investment, chemicals the classification may change based on UBA The practised hygienisation methods differ between the Baltic Sea Region countries. The most used methods are composting, lime treatment and pasteurisation. In Finland and Estonia, composting is state-of-the-art, while in Germany lime treatment is common. Some methods are not applied in the Baltic Sea Region, like solar drying and drying for agricultural use, aerobic thermophilic stabilisation and pre-treatment, and anaerobic thermophilic stabilisation.
Thermal conditioning is used but seldom for hygienisation, because the energy demand is much higher when primary sludge is also treated. Sludge drying Thermal drying is a technology that aims to significantly reduce the water content of sludge.
Drying is mostly used in large waste water treatment plants to increase the heat value of sewage sludge for incineration. Also, drying for agricultural disposal is possible, but not often practised because of its high costs.
The removal of water by evaporation from the treated and dewatered sludge increases the dry solids content of the sludge, and reduces both sludge volume and weight. Due to the high investment costs, it is usually restricted to large plants. The thermal drying process typically includes material handling and intermediate storage; it is preceded with sludge dewatering and sludge silos, and requires heat generation and distribution equipment, a thermal dryer unit, a biological filter for exhaust gases, a post-processing unit like pelletizing, and storage for the final product.
Thermal drying is based on the use of heat to evaporate water from the sludge after dewatering. The energy input in dewatering is much lower than in drying, thus a high DS content after dewatering is required.
Thermal drying processes are divided into two main categories — direct convection drying and indirect contact drying heating. This classification is based on how the thermal energy is applied to the sludge in order to increase the temperature. Principles of thermal drying.
Direct drying In direct drying of sludge, heat convection is achieved with direct contact with hot air or hot gases. Typical direct drying equipment is a rotary drum dryer or belt dryer. Indirect drying In indirect drying, a solid wall separates the sludge from the heat transfer medium, usually hot water, oil or steam.
Typical, indirect drying equipment include vertical tray dryers and horizontal disc, paddle or spiral dryers as well as fluidised bed dryers. Disk dryer in Gdansk, Poland. Photo: GIWK.
Summary of the main thermal drying methods Direct heating and indirect heating summary. Thermal drying is a well-known and a proven technology in central Europe where it has been applied on both large and medium scales. Solar drying is used in Bredstedt Germany. Sludge incineration Sewage sludge is a good fertiliser because of the high concentrations of phosphorus and nitrogen; however, it can also be a sink for contaminants.
In addition to various organic substances, heavy metals may end up in the sludge and pollute the environment. This is why sludge incineration has become more common in recent years. It is also possible to receive a positive energy balance out of incineration and utilise the calorific value of sludge. The main driver for sludge incineration has, however, been the fact that the amount of sludge generated at municipal waste water treatment plants is very large compared to the land area available for the disposal or treatment e.
The new directive will encourage the material recycling of sludge and limit the disposal of organic matter to landfills. The former requirement is likely to promote the disposal of sludge to agricultural land, provided that it is otherwise accepted by the farmers and competent environmental and agricultural regulatory authorities.
The latter requirement will encourage or oblige the sludge producers to incinerate sludge unless it cannot be otherwise disposed of. Incineration in Szczecin, Poland. Photo: ZWiK Szczecin. Sludge can be either co-incinerated with other sources of energy, such as municipal solid waste or fossil fuels, or mono-incinerated using other fuels only as support.
The design criteria for sludge incineration in different types of boilers depend on the mixture and heat values of different fuels. Sludge incineration is applied for digested, dewatered and possibly dried sludge. Sludge may be incinerated without drying and without digestion; however, in this case additional fuel is often required. Co-combustion The co-combustion of mixtures of different solid, liquid and gaseous fuels has been applied for decades and can thus be considered proven technology.
The incineration of municipal or industrial waste water sludges is more common in Germany and Finland than the other countries in the Baltic Sea Region. Both grate-firing and fluidised bed technologies are applied with co-combustion. Sludge and municipal solid waste co-incineration with grate firing are well-known and proven technologies in central Europe. This technology is not yet very widely applied in the Baltic Sea Region except for Germany, where co-incineration with coal has been practised in e.
Bielefeld, Bremen Farge, Duisburg and Veltheim. Mono-combustion Mono-combustion is usually designed for the simple destruction of sludge without energy recovery because the net heat value of sludge does not produce excess energy. If the sludge is digested, the heat value is even lower.
The mono-combustion therefore only consists of fuel reception, mixing and feeding systems, a furnace with burners of support and start-up fuels like oil, natural gas or coal, or biogas from digestion. Fluidised bed technology is, in practice, the only suitable technology for mono-combustion.
Sludge and solid waste incineration with fluidised bed technology are well known and proven technologies in industrial plants in the Baltic Sea Region. They have been applied in a few large waste water treatment plants for the mono-combustion of sludge, for example in Copenhagen, Denmark; St. Petersburg, Russia; and in Poland e. Summary of incineration methods Grate-fired and fluidised bed combustion. Disposal of sewage sludge or ash from incineration In the past, sewage sludge has been disposed to landfills, stored in huge sludge ponds, dried in the sun in arid climates or dumped to the oceans.
More recently, beneficial uses for dewatered sludge and ash from sludge incineration have been developed. In Europe and in the Baltic Sea Region countries there are various sludge disposal strategies in use.
Countries like the Netherlands, Belgium and Switzerland have forbidden or restricted the agricultural disposal of sewage sludge and is incinerated.
Other countries like Finland, Estonia and Norway use composted sludge for green areas, for example.
Some countries like Iceland, Malta and Greece are or have been completely disposing to landfill. In Russia and Belarus, collecting sludge to sludge pits or ponds is common. Source: Eurostat. Use in agriculture The use of municipal waste water sludge in agriculture has been practised in the Baltic Sea Region for at least 40 years.
The interest for agricultural disposal of sludge varies from country to country. Pollutants, as well as the possibility of hygienic contamination, have raised scepticism among the agricultural sector, politicians and the public towards the agricultural use of sludge.
New phosphorus recovery technologies are anticipated to allow the recycling of nutrients from sludge to agricultural use in the near future. Disposal to landfill In the European Union, a widely applied practice has been to dispose of the sludge that cannot be used in agriculture or landscaping to landfills. Landfills also require landscaping when a certain landfill area has reached its final height and sludge has been suitable material for this purpose.
The only quality requirement for landscaping landfills with sludge is that it cannot be in liquid form, corresponding to the general restrictions to dispose of any liquid materials to landfills.
The recent limitations or bans on the of disposal of biodegradable material to landfills will also limit the disposal of sludge to landfills and the use of composted sludge as a landscaping material in the long run. This limitation does not exist in the non-EU-countries. Disposal of sewage sludge ashes from mono-incineration Sewage sludge ash is the product of sludge incineration.
Only ashes from the mono-incineration of sludge and mixtures with other ashes with high concentrations of phosphorus and other nutrients can be used for further treatment and recycling.
Ashes from co-incineration have a very low concentration of phosphorus and possibly too high contaminant levels if co-incineration takes place, for example, with municipal household waste — and are usually disposed to landfill. Sludge burned in a cement factory does not have a disposal problem because the ashes are bound in the product.
Summary of the disposal methods Several methods to dispose of sludge exist; the sludge disposal strategies followed by each country in the Baltic Sea region are not uniform. The agricultural use of sludge or incineration and the disposal of ashes allow the utilisation of sludge as a material or energy resource; these are quite common methods in the region.
Composted or otherwise hygienised sludge is used in some countries in the region for green areas such as parks. The availability of nutrients in the sludge depends on the waste water treatment process in use.