Improving the effluent of small wastewater treatment plants by bacteria reduction and nutrient removal with an algal biofilm.

In wastewater ponds, bacteria numbers decrease considerably in the case of raised algae concentrations in the effluent. This shows that algae have a high potential for bacteria reduction in wastewater. Simultaneously, algae remove nutrients from the water for the formation of biomass. However, suspended algae also cause a high secondary pollution in the effluent of wastewater treatment plants. By using attached algae, as they are frequently observed as an algal biofilm in the effluent of wastewater treatment plants, the problem of separation of algae and water can be avoided. Furthermore, the algae can be removed simply from the water. In this study the possibilities for bacteria reduction and nutrient removal were examined with the aid of an algal biofilm. The results show that an algal biofilm process can be used for cases where small amounts of wastewater should be treated and a high quality of the effluent should be attained.

Bacteria reduction and nutrient removal in small wastewater treatment plants by an algal biofilm.

Attached algae settlement is frequently observed in effluents of wastewater treatment plants at locations with sufficient sunlight. For their growth they incorporate nutrients and the surface of the algal biofilm accumulates suspended solids from the clarified wastewater. During the photosynthesis process of algal biofilms oxygen is produced while dissolved carbon dioxide is consumed. This led to an increasing pH due to the change of the carbon dioxide equilibrium in water. The high pH causes precipitation of dissolved phosphates. Furthermore an extensive removal of faecal bacteria was observed in the presence of algae, which may be caused by the activity of algae. The experimental results indicate the high potential of these attached algae for polishing secondary effluent of wastewater treatment plants. Especially for small wastewater treatment plants a post connected stage for nutrient removal and bacteria reduction can be developed with the aid of an algal biofilm.

Innovative technologies for wastewater treatment in coastal tourist areas.

The selection of appropriate wastewater treatment technologies for coastal tourist areas is important in the sense that they have to meet stringent effluent limits in a simple and easy to operate flow scheme. This paper outlines different effluent standards implemented in sensitive coastal areas and briefly discusses the merit of a number of innovative technologies, namely the sequencing batch reactor, the intermittent aeration process, the moving bed reactor and the biofim-filter-sequencing batch reactor system, either as a batch or continuous flow process applicable in these areas.

Polishing of secondary effluent by an algal biofilm process.

The potential in polishing secondary effluent by an algal biofilm composed of different green and bluegreen algae was investigated. During the photosynthesis process of algal biofilm oxygen was produced while dissolved carbon dioxide was consumed. This led to an increasing pH due to the change of the carbon dioxide equilibrium in water. The high pH caused precipitation of dissolved phosphates. The attached algae took up nitrogen and phosphorus during the growth of biomass. In addition to nutrient removal, an extensive removal of faecal bacteria was observed probably caused by adsorption of the algal biofilm and by photooxidation involving dissolved oxygen. The experimental results suggest that a low-cost, close to nature process especially for small wastewater treatment plants for nutrient removal and bacteria reduction can be developed with the aid of an algal biofilm.

Activated carbon and residual nitrification for higher quality effluents for the coastal areas.

Efforts for the task of modification of a nitrification/denitrification unit operating in a series of two fixed bed columns are outlined. The problem was elevated dissolved oxygen concentrations at the entrance of the denitrification column, resulting in an excessive consumption of methanol. The possibility of using a column of activated carbon for adsorption alone and in which both adsorption and residual nitrification take place was investigated. The results were observed to be very satisfactory in reducing dissolved oxygen levels to practically zero at the entrance of the denitrification unit especially for the case where both adsorption and residual nitrification were employed.

Membrane dosing units for chemicals in water and wastewater treatment plants.

It is well known that in the practice of the drinking water as well as of the wastewater treatment especially for the processes of pH-regulation, flocculation, precipitation or disinfection, the dosing of reagents is necessary. The costs of the automatic dosing stations are comparatively high. For the smaller water treatment plants these stations are uneconomical and charged with maintenance problems very often. In many cases the frequently observed highly fluctuating reagents needs and the recess between can cause disruption of the normal exploitation work. These disadvantages can easily be overcome by a device based on permeable or semi-permeable membranes. The use of semi-permeable membranes is favourable especially in the cases of fluctuating water quantities or standstills. It can be effective because of the possibility for their self-regulation during the dosing. When there is no inflow available some kind of concentration equilibrium is established between the internal and external membrane layers. This system is easy to install and it can be easily adapted to the local conditions. The device can be a canister filled with the desired reagent and covered with a lid of a definite semi-permeable membrane. After determining the permeability of the membranes made of different materials only the appropriate membrane area is important to be determined. Developed methods for defining the specific membrane permeability are discussed in the paper. Suggestions for the application of such devices in practice are given as well.

Early warning-system for operation-failures in biological stages of WWTPs by on-line image analysis.

By the observation and evaluation of the microscopic picture of activated sludge samples it is possible to introduce another biological parameter additional to conventional physico-chemical parameters for the control of biological stages of waste water treatment plants. Considering the fact that parameters like floc size and floc size distribution, structure of the flocs (compact/open), shape of the flocs (round/irregular) allow perceptions of the adjusted operation conditions of the biological stages, evidence for changing operation conditions or threatening operation disturbances can be recognised. This recognition takes place at a very early phase, because the morphology of activated sludge flocs reacts very fast to changing conditions. An automatic image analysis of activated sludge floc pictures would enable the introduction of a new sum parameter to enhance operation control of aeration tanks. By a statistical evaluation of the processed sludge images several parameters can be used to describe the alteration of activated sludge flocs characteristics. With these biological parameters it is possible to detect altered operation conditions or threatening or existing operation problems at an early phase. Thus it is possible to plan suitable countermeasures. Furthermore, the microscopic picture is the only parameter, that gives important information about the structure of the activated sludge flocs and the biozenosis. In comparison with the mainly used physico-chemical parameters, that just give information about the inlet and outlet of the wastewater treatment plants, the microscopic picture is the only parameter that gives information about the biology of the wastewater treatment process. By means of this biological parameter an improved control and regulation of the biological stages of wastewater treatment plants can be obtained.

Sustainable development of wastewater treatment strategies for the food industries.

The sustainable development of environmental protection is a newly created philosophy. It means continuous development of better protection of the air, soil, water and resources, used from the industry, to be saved also for future generations. The globalization of the economy is another process, which interferes with environmental ideas, and an equilibrium with the socio-eco-sustainable development is wanted. The industry is subjected to big changes depending on economic development. Thus the treatment plants at the end of the pipe must be constructed with maximum flexibility. A removal of constructed devices, if not necessary, must be considered from the beginning as a possibility. Priority is given to integrated production processes solving wastewater problems directly by production devices. The treatment of the process wastewater streams separately will become more important. The end of the pipe solutions will be less complicated and more reliable. The reuse of valuable waste substances and treated water will reduce the total cost of the treatment plants substantially.