Sludge Watch ==> Guy Architects talk about Composting Toilet Technology

[maureen.reilly at sympatico.ca]

Sludgewatch Admin:

This is an interesting run down on composting toilet and related green 
technologies.
You may wish to read the whole article on sustainable development 
technologies at:

http://www.ewire.com/display.cfm/Wire_ID/3204

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Guy Architects Ltd reviewed the ways in which green technologies could be 
incorporated into the general housing market.

CANADA, Jul. 11 -/E-Wire/-- 1.0 ARCHITECTURE Guy Architects Ltd reviewed the 
ways in which green technologies could be incorporated into the general 
housing market. The following is a review of sustainable technologies we 
considered for incorporation into a prototype housing design. The litmus 
test for the selections of systems......




3.0 COMPOSTING TOILETS

Composting toilets are systems which treat human waste by composting and 
dehydration to produce a useable end-product that can be valuable soil 
additive. They come in a variety of models and brand names as well as 
different shapes and designs to enhance and optimize the natural composting 
process. They use little or no water, they do not need to be connected to 
expensive centralized sewage systems and so no piping is required. They 
cause no environmental damage and they produce a valuable resource for 
gardening. These systems can be broadly divided into two different types: We 
selected a composting toilets for use in the prototype house for the 
following advantages:


Unusual Sites Composting toilets can be installed in many different 
situations which would not accommodate other systems, such as sites that are 
rocky or swampy, have a high water table or no water storage, are 
environmentally sensitive or are close to running watercourses. All these 
difficult site situations can be accommodated with a small amount of 
alteration to the basic system design.


Reduction of Odour Problems The suction air flow in most composting systems 
takes toilet and bathroom odour out of the room and acts like a constant 
extraction fan.


End Product Recycled While it is small in volume, the solid end product is a 
valuable humic fertiliser that can be utilised around trees and gardens.


Reduced Grey Water Loading Where composting toilets are installed instead of 
septic or mini-treatment systems, there is a large reduction in the 
"loading" on the effluent treatment system by the removal of "black-water." 
Smaller, lower maintenance grey-water systems can therefore be used.


Recycling A composting system offers the capacity to recycle a significant 
amount of the household waste. Food scraps, paper, lawn clippings and grease 
from grease traps and grey-water systems can be composted back through the 
toilet. If a reed bed grey-water system is installed and is available, then 
a complete wastewater treatment system is possible at relatively low cost. 
There is no wastage in the system.


Reduced Marine Pollution Nutrient load on surrounding streams and rivers are 
almost negligible using a composting system. This results in more oxygen 
being available in the water and a return to improved activity of marine 
life.





Less Environmental Impact Compared to centralized sewage systems, on-site 
composting and grey-water treatment has less impact on the environment;


· Large effluent releases and other discharges into watercourses and oceans 
are avoided


· Disruption to the environment through piping installation is eliminated


· Leakage of raw sewage into groundwater through pipe deterioration and 
breakage is eliminated


Flexibility in Estate Planning By eliminating the planning constraints of 
the sewage system's underground piping and infrastructure, housing 
developments can be designed with more emphasis on environmental and social 
considerations, rather than how to best situate the blocks to make pipes run 
straighter.


All composing toilets carry out this basic process of aerobic decomposition. 
Design variations have been developed to enhance this process and they 
include:


· baffles for increasing the efficiency of air distribution in the pile


· heating elements to keep the compost at the optimum temperature


· injecting air for increasing the decomposition rate


· mixing tongs to ensure homogeneous decomposition throughout the pile


· the addition of composting worms and macro-organisms to speed treatment


There are a wide variety of systems including:


· Owner-built, two chamber composting systems that are simple, but 
effective.


· Owner-built from concrete blocks and with a concrete lined, inclined base. 
These systems are constructed inside the house's foundations.


· Manufactured, large tank, inclined base models suitable for heavy 
loadings.


· Wide variety of small units which fit into existing bathrooms. Many of 
these units come equipped with dehydration fans and heaters.


· Vacuum flush units for the production of worm castings.


· Full flush systems with centrifugal action to deposit wastes into 
composting chamber. There are two types of systems, the Batch System and the 
Continual Process Systems. With the batch systems, a container is filled and 
then replaced with an empty container. The composting process is completed 
inside the sealed container. The system may have a single replaceable 
container, or it may be a carousel system where three or four containers are 
mounted on a carousel. A new container is spun into the toilet area when the 
other is full. After a full cycle is completed, the first container is fully 
composted and ready for emptying.


With the continual process system. These systems are in a constant state of 
composting. "Deposits" are put into the system, composting reduces the 
volume and moves it downward where it is harvested after 6-12 months as 
fully composted material. All systems are designed to treat the organic 
"deposits" by composting, worm processing, micro- and macro-organism 
breakdown and dehydration and evaporation of moisture.


We selected a continual process system for the prototype design for the 
advantages mentioned above and the fact that the system is viable within a 
LEED standard Green Building.


System Diagrams


The schematic shown on the right represents a typical installation of a 
composting toilet system. The composting chamber must be mounted directly 
below the toilet. The purpose of the composting chamber is to maintain 
optimum conditions for the micro organisms responsible for composting the


Diagrams of some of the most popular commercially available composting units 
are shown . The unit, shown on the left, contains a rotating drum to 
constantly mix the contents of the chamber so that all of the organic wastes 
are completely aerated.


4.0 WATER MANAGEMENT SYSTEM All water and wastewater flows into and out of 
the building can be managed as a closed system. Most locations in Canada 
will receive from 50 to 125 cm of rain per year. Rainwater captured from the 
roof of most single family structures will be able to provide about 100 m3 
of fresh water per year. Therefore it is possible for reclaimed rainwater to 
supply at least a significant portion of the total water needs of a typical 
LEED Standard Green Building with the use of medium sized storage tanks. 
Lower water using fixtures are used for sinks and showers with a flow rate 
about 0.5 US gallons per minute (gpm) . With potable water at a premium, the 
best conservation scheme is to use non-potable water for landscape 
irrigation. This is accomplished through a combination of rainwater, 
municipal supplied water or pumped groundwater (if available), and water 
from treated grey water produced by the on-site biofilter. This system has a 
100% separation of potable and non-potable in all pipes and storage tanks. 
The addition of water storage tanks to the building design adds some 
additional costs to the construction, but also provides a number of 
benefits. For example, the inherent coolness of the water means that water 
can be circulated through the building's cooling as a low cost way of 
cooling the building in summer.


Waste Water Treatment The first step in wastewater treatment is to minimise 
the volume of wastewater that has to be processed in the first place. The 
second step is to re-use as much of the processed water as possible within 
the building for applications such as toilet & urinal flushing and landscape 
irrigation. Reusing the reclaimed water for toilet & urinal flushing 
requires water treated to Class 4 standards, essentially drinking water 
standards.


In a conventional building, the water use can be represented as follows:


Conventional buildings operate totally on potable water, typically treated 
and filtered, for moving human and food preparation waste out of the 
building into the sewer system. In many urban areas, there is a 
long-standing problem of combined sewer overflows during periods of higher 
than average rainfall means that every new building without on-site water 
recycling adds to the pollution of nearby natural bodies of water.


The Prototype wastewater treatment system is located in the basement of the 
building and will be hooked up to a septic system or the local sewer system 
in case of emergency overflow or for periodic sludge discharge. The system 
is designed so that the treatment process requires very little occupant 
attention. With the exception of solids (sludge) discharge and an annual 
membrane cleanout, the system can operate virtually unattended.


The sewage treatment plant has to provide both anaerobic and aerobic 
treatment of wastes, before final polishing and disinfection. The resulting 
Class 4 water will be of drinking water quality. A small amount of sewage 
solids needs to be discarded on a periodic basis. The complete bioreactor 
flow diagram is shown below:


The main problem with the above comprehensive system is that it is very hard 
to justify the significant added expense for a single-family habitation. For 
this reason, this type of system is usually only justifiable in larger 
commercial buildings and not for single family homes. The better and more 
economical approach is use in the prototype in which composting toilets 
treat sewage wastes and a water biofilter treats grey water. Our system is 
described below.


Each building, Green or not, will produce a significant volume of non-septic 
wastewater each day from showers, baths and sinks. While the daily volume of 
grey water is significantly reduced in Green Buildings, careful 
consideration must still be given to the on-site treatment of this liquid 
waste product. While it is not necessary to treat this water to the same 
extent as sewage, this grey water should not be discharged directly to the 
environment without some treatment. In fact, LEED standards require that all 
of the grey water produced by the building be recycled and reused on site.


Pre-manufactured mechanised systems are independent of the environment and 
will perform consistently if continually maintained. However, this 
maintenance is more than the typical homeowner (or organisation) is willing 
to undertake and treatment performance may be compromised.


Consistent with the low-maintenance, appropriate-technology focus desired by 
our team. We proposes a single pass biofilter has been developed to provide 
consistent aerobic renovation independent of the environment with low effort 
and with virtually no maintenance requirements.


The Absorbent Biofilter renovates domestic grey water in a small contained 
volume because of the particular physical properties of the synthetic filter 
medium. In contrast to soil and sand media which must be loaded with 
wastewater, allowed to drain and then allowed to aerate before loading 
again, the medium provides separate flow paths for wastewater and air. This 
characteristic enables simultaneous loading and ventilation which in turn 
permits much higher loads of waste water compared to a tile bed or sand 
filter, without sacrificing effluent quality. The medium readily handles 
surge flows and does not plug even at high loading rates. A diagram of the 
system is shown below: The biofilter is contained in a covered fibreglass or 
concrete tank and is insulated with Styrofoam sheets. A small fan circulates 
air through the medium by way of ventilation pipes. The biofilter medium is 
about 1 m thick. Tests have demonstrated that this biofilter is capable of 
removing an average of 97% of TSS in the effluent at a loading rate of 
 >1,500 L/day. The BOD removal averages > 98%. This system is capable of 
handling surges in wastewater flows and oscillations in nutrient loading and 
temperature. Nitrogen species are thoroughly oxidised to nitrate in the 
field unit. Removal rates of fecal and total coliforms average 99.6%. A 
typical household would require a 3 m3 biofilter to renovate >1,500 L/day in 
cold climates and less in warmer areas. Treated water with BOD and TSS 
typically < 1 mg/L could be stored in an ordinary water tank for use within 
the structure. The unit can operate without a ventilation fan if complete 
nitrification is not required.


An alternate design for the treatment of grey water is shown below:


This wastewater biofilter design consists of two concentric cylinders toped 
by a porous media filter. Liquid effluent flows into the bottom of the inner 
cylinder and is then pumped upwards and then sprayed onto the porous media 
above it. As the liquid trickles down through the randomly packed media, 
aerobic Nitrosomonas bacteria living in the bio-film coating each of the 
particles convert the ammonia in the wastewater into nitrates. The liquid 
then drips through the porous media into the outer cylinder where anaerobic 
Nitrobacter bacteria transform it into nitrogen gas that is vented to the 
outside air. Such a biofilter is capable of reducing nitrate concentrations 
in the inlet wastewater by up to a factor of ten.


This simple and economical system has many attractive features; therefore it 
can be put forward for further consideration in a LEED certified Green 
Building.


It is possible to add an additional treatment stage to clean the purified 
water outlet still further. A small greenhouse or glazed enclosure can be 
built to house a biological treatment system. Inside the enclosure, water 
treatment occurs in a series of linked hemispherical tanks that contain a 
variety of ecosystems, including bacteria, algae, floating plants, snails 
and fish that process the water before it goes through an artificial marsh. 
An artificial marsh is similar in function to the processes that occur in 
natural wetlands. Water flows by gravity from one tank to the next. These 
tanks contain algae, zooplankton, phytoplankton, snails, bloodworms and 
specially selected aquatic and non-aquatic plants. The tanks can be aerated 
to keep bio-solid particles suspended in the water, making them readily 
available for consumption by organisms and plants. As the wastewater slowly 
flows from tank to tank, the organic constituents become food to the 
organisms present in the containers. As it moves up the food chain, much of 
the organic mass is eventually converted to basic constituents such as 
carbon dioxide, water and energy. That portion of the mass that is converted 
to animal and vegetative growth is periodically harvested and composted.


The wastewater drains by gravity from clarifying tanks to a swirl separator 
that helps remove most of the remaining solids (mostly plant matter). Sludge 
from this clarifying process can be digested aerobically in an underground 
sludge tank, thickened, decanted and then applied to an outdoor reed bed 
composting system. Both the under drain from the reed beds and decant liquid 
are returned to the blending tank. The thickened sludge is applied to the 
reed bed in very thin layers. The reeds serve to further breakdown sludge 
anaerobically over a period of weeks, eventually producing a benign and 
fertile soil amendment.


In the final stage, effluent from the clarifying tanks flows by gravity 
through a sand filter or micro-screen before flowing into an artificial 
marsh constructed of gravel. This marsh is planted with a variety of marsh 
grasses, flowers and plants. The marsh is a point of denitrification, 
nutrient uptake and phosphorus absorption. Effluent can be discharged into 
rivers, streams, or onto the ground surface depending upon local 
regulations. In some jurisdictions, effluent is being used for crop 
irrigation and drinking water for cattle. The effluent can be used for 
watering lawns, supplying fire hydrants and for flushing toilets. The final 
effluent meets the highest standards of wastewater treatment.


The greenhouse/glazed enclosure simply acts as a barrier from the natural 
environment preventing precipitation from being unnecessarily processed, as 
well as regulating inside temperatures necessary for living organisms to 
thrive throughout the year. In this approach to grey water treatment, 
organic materials in the water are not seen as waste products, but as food 
that is used by the biological community living within the greenhouse. A 
schematic of the proposed treatment system is shown below.


Water Heating: Heat is extracted from laundry and shower water through a 
heat exchanger on the drain. This served as a preheat for the Domestic Hot 
water(DHW) lines. Additional heat as required is provided by an on-demand 
hot water heater. Water preheat lines also extract heat from the Trombe wall 
via a heat exchanged during the warmer seasons.