Consider this: a city decided to build a wastewater treatment plant so that they can get rid of septic tanks throughout the city, which are overflowing or contaminating the groundwater aquifer by percolation and seepage. The current situation is so bad that potential industries and commercial enterprises are rethinking if they should consider moving into town where adequate facilities for the wastewater generated by them do not exist. Instead, they consider another location for its operations. Every day, the city is in the news that its wastewater overflows are contaminating the environment and polluting the once-pristine stream running in the middle of town that had provided recreational facilities to its citizens. The citizens are up in arms for its poor record on environment.
The main photo above was shot by rye'n on Flickr. View a high resolution of the image on Flickr.Now come a series of questions. What type of plant should it be? What technologies should the plant use? What should be the capacity of the plant? From where should the money for its design and construction come? Would it require legislation for passing user fees and how will the citizens accept these charges? The list goes on and on. Perhaps, a good, experienced and competent consulting firm can assist the city in addressing all these issues.
But a big question still remains. Where should the plant be located? Everyone will say NIMBY i.e. NOT IN MY BACKYARD. Everyone associates a wastewater treatment plant with odors, chemicals with possible health effects, noise caused by machinery, traffic resulting from trucks moving in and out, tanks sticking up and being visually obtrusive, plain concrete and/or steel structures, and overall unaesthetic appearance. All these issues, if not addressed properly, will undoubtedly degrade the neighborhood and adversely affect property values. True or False?
All these concerns can be reasonably addressed by a competent and environmentally conscious consultant team. The team needs to have good and competent process engineers; architects; landscape architects, civil, structural, mechanical engineers; planners; environmentalists; public- relations experts; and civic-minded professionals on board. A modern treatment plant can be and should be a good neighbor to the adjoining residences and enterprises-commercial as well as industrial if applicable.
This paper contains some examples where most of these concerns existed, but were addressed to the satisfaction of concerned neighbors.
No one wants to have his or her home near a wastewater treatment plant, regardless of how well the plant is designed and is aesthetically acceptable. But calling it by a different name could mitigate that concern. Consider naming it a water reclamation plant, water conservation plant, water recycling plant or water factory instead. This could mitigate, if not eliminate, that concern. Sometimes, it could simply be a perception issue, which can be addressed by giving the facility a different catchy name. Most plants in the U.S. today are renaming their facilities with those listed earlier. A plant in Orange County, California, for instance named its plant Water Factory 21.
A good layout can often be helpful in public acceptance of the project. Consider the following:
Selection of treatment processing, among other factors, should consider which processes are less amenable to generation of odors. For example, membrane bioreactors (MBR), by virtue of their smaller footprint, may be a better treatment process than conventional activated sludge. In small size plants, with MBRs, it may be possible to eliminate primary clarifiers, which often generate more odors than other processes at the plant. A similar criterion can be used in the selection of sludge handling processes. This may involve eliminating gravity sludge thickeners, or using centrifuges or screw processes with integral covers instead of belt presses, as an example.
This is often a major concern. How can a wastewater treatment plant not cause odors? This is what the citizens have always believed, and they probably are right. They have likely visited some old plant designed at a time when either the odor was not an issue (remote location perhaps) or the technologies to confine and treat odors were not available.
Now, wastewater professionals understand both the chemistry of odors as well as the means to confine and capture odorants and treat them. There are several technologies that have been developed&#;both proprietary and non-proprietary&#;that can reduce odors to levels barely discernable by humans. Wastewater professionals now fully understand the chemistry of odors&#;such as sulfides, mercaptans etc.&#;and therefore know how to treat them biologically and/or with chemicals.
Most modern plants are opting for biological scrubbers due to the facts that no chemicals are required thus reducing the carbon foot print of their plant; they are not as tall, thus have lesser visual and obtrusive impact; and they can scrub nearly all odor-causing compounds&#;whatever their origin&#;if properly designed with adequate residence time unique to the nature of odorants to be removed. In fact, these scrubbers can be designed to be aesthetically pleasing&#;even underground or sticking a couple of feet above ground and mildly landscaped at the top. The media can be compost, wood chips, bark, peat, lava rock, or any combination of the above materials. For sensitive neighborhoods, these scrubbers can be followed by an adsorption scrubber using activated carbon as the adsorption media for final polishing.
After important basic knowledge about wastewater treatment with small sewage treatment plants in parts 1 and 2 of our knowledge series and the explanation of common cleaning processes and plant types in parts 3 and 4, things are now getting really exciting again with the most advanced systems and processes. Especially in times of climate change, what counts in wastewater treatment is performance, economy and efficiency - after all, water protection is climate protection. Contemporary methods of wastewater treatment are more popular than ever...
#Membrane bioreactors are operated with a free-floating #biomass. The microorganisms combine to form #sludge flakes, which can have different sizes depending on the #aeration process. The required aeration is generated with a compressor and fed into the #bioreactor via #membrane aerators. A #secondary clarifier is not required, since the water is drawn off from the bioreactor via #membrane filters.
The systems are approved where #wastewater has to be disinfected or #disinfection is required: discharge into bathing lakes or into #water protection areas are some applications. With #wastewater treatment, the #effluent classes C (#carbon decomposition), N (#nitrification) and H (#hygienization) can be achieved.
Special system features
Due to their #biomass structure, membrane bioreactors have a very good utilization of the reactor volume in relation to all other systems - the volume of the bioreactor is relatively small compared to other systems. Short-term load surges, which can occur especially in small sewage treatment plants up to 8 inhabitants, can therefore lead to a temporary deterioration in the cleaning performance. The ventilation must be designed in such a way that both the oxygen demand of the #microorganisms is covered and permanent #sludge deposits are prevented. The ventilation must also be designed in such a way that the air flow can keep the filter surfaces clean. In contrast to #biofilm systems, the multiplication rate of the microorganisms is much higher, so that the biomass can adapt more quickly to different dirt loads. Several filter plates are combined into blocks. The filter material consists of a plastic-coated carrier material with very fine pores, which are also able to retain harmful bacteria. The #water to be drained is usually sucked through the filter by pumps. The filter must be cleaned with chemicals at least once a year by a maintenance service.
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Based on previous experience, the filter blocks must be completely replaced after 5 years. If the filter is intact, #turbidity is also removed from the wastewater. If filter plates are used instead of ceramic modules, the costs for cleaning them are lower.
What should be given special attention?
#Sludge drift from the #primary treatment must be prevented, as this can clog the spaces between the filter plates. Mechanical damage prevents the sterility of the draining water. Certain substances in the waste water, e.g. fats, can lead to early clogging of the filter material, so that cost-intensive cleaning at shorter intervals can become necessary. So that an increasing clogging of the membrane is detected at an early stage, a corresponding measuring device with an alarm that measures the negative pressure in the suction system is actually a matter of course. Damage to the filter material can also be detected by this measuring device due to a pressure drop in the suction system. A decrease in the air performance of the system or longer switching off of the ventilation leads to the #membrane gaps becoming blocked. The #membrane plates can then usually no longer be cleaned and must therefore be renewed.
What are the controls like?
If the water level in the bioreactor is too high, this could be a sign that the filter material is clogged or an above-average amount of wastewater has flowed into the #sewage treatment plant. In such cases, a backflow into the house is prevented by an emergency overflow, which is usually available. However, valuable #activated sludge or untreated wastewater from the preliminary treatment gets into the outflow, which can result in consequential damage in the form of #environmental pollution. If the water level is too high, the maintenance service must be informed.
Diese Anlagen werden mit einer freischwebenden Biomasse betrieben. Die Mikroorganismen schließen sich zu Schlammflocken zusammen, die je nach Belüftungsverfahren unterschiedliche Größen haben können. Im Gegensatz zum #Biofilm kann der Fachmann über Farbe, Form, Geruch, Menge und #Absetzverhalten der Schlammflocken den Zustand der Anlage mit bloßem Auge beurteilen. Die erforderliche Belüftung wird mit einem Luftverdichter erzeugt und über gelochte Membranbelüfter in den Bioreaktor geleitet. Weitere Belüftungsmöglichkeiten bieten Tauchmotor-, Injektor- und Oberflächenbelüfter. Je nach Anlagentyp sind eine oder zwei Pumpen für den Wassertransport erforderlich. Einige Hersteller verwenden zusätzlich noch Magnetventile. Bei dieser Art der Abwasserreinigung können die Ablaufklassen C (Kohlenstoffabbau), N (Nitrifikation) und D (#Denitrifikation) erreicht werden.
Special system features
Due to their biomass structure, SBR sewage treatment plants have a very good utilization of the reactor volume compared to biofilm plants. Due to the prescribed dimensioning of the bioreactor in small sewage treatment plants, these plants can process at least twice the dirt load for which they were designed. However, the ventilation and the possible additional hydraulic load must be adapted to these conditions. The aeration must be designed in such a way that both the oxygen requirements of the microorganisms are covered and permanent sludge deposits are prevented. In contrast to biofilm systems, the multiplication rate of the microorganisms is much higher, so that the biomass can adapt more quickly to different levels of pollution. #Activated sludge treatment plants are not so sensitive in terms of sludge removal from the primary treatment. For this reason, more sludge can be stored in the primary treatment than in biofilm systems. Compared to activated sludge treatment plants, which work in a continuous flow process, the SBR process is less sensitive to larger amounts of water flowing in for a short time, as there is a buffer volume. An additional secondary clarifier is also not required, since there is no aeration during a limited phase and the activated sludge can settle undisturbed. After this phase, part of the cleaned water is pumped from the upper part of the system into the drain. After the pumping process has been completed, the space in the bioreactor that has become free is charged with the pre-cleaned wastewater from the #settlement pit. These plant systems can usually be easily retrofitted in existing #septic tanks.
What should be given special attention?
If the discharge point is higher than the sewage treatment plant outflow, there is no need for an additional pump shaft in systems with electrically operated pumps. Function, cleaning performance and energy saving are largely dependent on intelligent software. The function of the system is only guaranteed if all aggregates are functional. The number of built-in pumps, compressors and solenoid valves depends on the manufacturer. The number of electrical units is between two and five.
What are the controls like?
If all malfunctions are recognizable via alarms, only the legally prescribed operator checks need to be carried out.
#CBR plants are operated with a free-floating biomass. The microorganisms combine to form sludge flakes, which can have different sizes depending on the aeration method. In contrast to biofilms, the specialist can assess the condition of the system with the naked eye based on the color, shape, smell, quantity and settling behavior of the sludge flakes. The necessary aeration is generated with an air compressor and fed into the bioreactor via perforated membrane aerators. In wastewater treatment, effluent classes C (carbon degradation), N (nitrification) and D (denitrification) can be achieved.
Special system features
Due to their biomass structure, #CBR sewage treatment plants have a very good utilization of the reactor volume compared to biofilm plants. Due to the prescribed dimensioning of the bioreactor in small sewage treatment plants, these plants can process at least twice the dirt load for which they were designed. The ventilation and the possible additional hydraulic load must be adapted to these conditions. The strength of the aeration must be designed in such a way that both the oxygen requirements of the microorganisms are covered and permanent sludge deposits are prevented. In contrast to biofilm systems, the multiplication rate of the microorganisms is much higher, so that the biomass can adapt more quickly to different levels of pollution. Compared to activated sludge treatment plants that work in a continuous flow process, the CBR process is less sensitive to larger amounts of water flowing in for a short time, as there is a buffer volume. The built-in throttle orifice in the drain separator prevents the treated waste water from draining off prematurely. The usual sludge retention via a secondary clarifier is no longer necessary. This task is performed by the much smaller outflow separator, which is housed in the bioreactor. The total volume required is slightly less than that of an SBR plant. The excess sludge that occurs is drawn off by an automatic siphon before the start of aeration. The built-in #float switch determines the point in time for economy operation and regulates the #nitrogendegradation. In the event of disproportionately large amounts of water accumulating, an alarm condition is also triggered. The technical equipment is very small due to the system, so that the system control can be easily built. The only electrical unit is an air compressor, which ensures that the microorganisms are supplied with oxygen via a hose aerator in the reactor. These plant systems can usually be easily retrofitted in existing septic tanks.
What should be given special attention?
If the discharge point is higher than the sewage treatment plant outlet, the difference in height must be bridged with an additional pump. Simple system operation only requires the maintenance company to readjust the ventilation times (in the event of a change in the number of residents who are permanently present).
What are the controls like?
Only the statutory operational controls have to be carried out.
The #UV disinfection is usually preceded by an #SBR treatment plant. With this plant constellation, the effluent classes C (carbon degradation), N (nitrification), D (denitrification) and H (hygienization) can be achieved for the first time. The systems are approved wherever sterilization of the waste water is required. Discharge in bathing lakes or in water protection areas are some applications.
Special system features
During the pumping process from the SBR plant, the water is guided through a system of pipes past a UV lamp that emits a wavelength of 254 nm. The water throughput is set in such a way that harmful bacteria are killed by the UV effect. Since the full power of the UV lamp is only reached after a burning time of 5 minutes, it is ignited in good time before the pumping process and then switches off again. Compared to the MBR system, the power consumption here is relatively low. The UV device can be housed in an outdoor cabinet or in the shaft of the sewage treatment plant. The service life of the lamp is - depending on the lamp type - several years. The tube of the UV lamp must be cleaned at every maintenance. Since no filter is used in this system, there is no risk of backwater when the cleaned waste water is discharged.
What should be given special attention?
The UV lamp should be attached in such a way that it can be easily removed for cleaning. A warning device for recognizing the timely replacement of lamps is mandatory. For optimal disinfection performance, the water flow rate must be throttled using a slide according to the manufacturer's specifications.
What are the controls like?
No.
That was the fifth and last part of our series "Everything about wastewater treatment and small wastewater treatment plants" - from the basics to individual cleaning processes and types of plants, from basic knowledge to processes and systems that are advisable in times of climate change.
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