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Composting and Maturing of Human Residual Products Contained in
Drained "Black" Wastewater
In the autumn of 1998 the County of Storstrøm initiated the project "Composting
and maturing of human residual products contained in drained "black"
wastewater".
Chapter 1: Introduction
In order to illustrate how human residual products can be recycled through composting
in Denmark, Storstrøm County has initiated a project funded by the Danish Environmental
Protection Agency programme on sustainable urban renewal and wastewater treatment. The
project was originated by the Kjær family in the municipality of Stubbekøbing, by A
& B Backlund ApS and by Storstrøm County, who jointly developed and planned the
project.
One of the goals of the project is to collect experience on establishing and using a
source diverting compost toilet system in a one-family house. Another goal is to collect
experience on the use of a source collecting compost toilet system including many users,
experience from both operation staff and users. The intention is, moreover, to survey the
composting process in the two toilet systems, e.g. in order to assess the quality of the
compost material.
In the autumn of 1998, a new wastewater system was established in Stubbekøbing. The
system is based on system assemblies, commercially available but not yet tested in
Denmark. The examinations of the system were made during the period November 1998 -
October 2001.
The source-collecting toilet at the Skelsnæs Pavillonen was established in 1998,
before the project was launched. The examinations of the system were made in 1999 and in
2000. A questionnaire study among the users was made in the summer season of 2000.
Chapter 2: Examination programme
In this chapter the examination programmes of the two localities are described. Based
on interviews and supervision, the examinations include the experience gained from the
installation and operation of the source segregation toilet system compared to the
operation of the source collecting toilet system. Furthermore, the results of the
measurements taken from the compost of the source diverting system are examined.
The analysis focuses on the examination of the functionality and stability of the
systems as well as on measurements of the content of nutrients and special micro-organisms
in the compost material. The analyses of the micro-organisms and nutrients are made
exclusively with material collected in the source diverting system, as the composting
process of the source collecting system at Skelsnæs Pavillonen is interrupted at such an
early stage that the material must be regarded as night soil.
Since the co-ordinated measuring programme of selected theme-3 projects is expected to
include analysis of the content of heavy metals and xenobiotic components, these are not
included in the analysis.
Chapter 3: Human urine and faeces
This chapter characterises urine and faeces on the basis of the constituents. Even
though urine and faeces normally constitute approx. 1-1.5% of the household wastewater,
they account for 91% of the discharge of N, 83% of P, and 60% of K. Urine alone accounts
for 80% of N, 55% of P, and 44% of K contained in the household wastewater (Sundberg 1995,
Vinnerås 2001).
Standard urine production is indicated to be 365-550 kg per person per year depending
on the source. The annual standard amount of faeces varies from 33 kg per person in
Vinnerås (2001) to 110 kg per person in Del Porto (2000). The content and composition of
nutrients in the faeces make them suitable as fertilisers, even though the content of N is
somewhat lower compared to the need. It is, however, not the output variables of the
faeces, but the nutritive content of the end product that is decisive for the manurial
value.
Composted faeces may also be useful as soil improving material. It may have a great
effect on especially barren lands containing much clay or sand. Composting will increase
the content of carbonaceous organic material of the soil, which leads to an increase of
the water-retaining capacity and the accessibility to nutrients. Humus produced during the
composting process also creates good conditions for a healthy population of organisms in
the soil, protecting the plants from earthborn diseases (Kalkoffen et al. 1995, Esrey et
al. 1998).
Human faeces contain a large amount of bacteria, which does not necessarily imply a
large quantity of infectious matters, however. Infected persons do, however, secrete large
quantities of infectious matters with the faeces. In the composting process of faeces it
is therefore important that the amount of indicator bacteria and actual infectious matters
is reduced to an acceptable/defined level.
Chapter 4: Composting and compost toilet systems
The chapter gives a short description of composting, composting processes and compost
toilet systems, as an overall presentation of the material. However, the references listed
may give an overview of concrete models and experience gained from the operation.
Making compost is a process in which the material is transformed by the aid of oxygen.
The organic part of the wet residual/waste products is mineralised or transformed into
solid humus by the aid of oxygen-consuming micro-organisms, releasing carbon dioxide and
water in the process. A humidity percentage of 45-70% in the compost substance is ideal to
the process (Del Porto et al. 2000). The composting process can be divided into three
phases: decomposition, rebuilding and construction. The substance is reduced considerably
during the process, which at best results in a compost substance of a characteristic dark
colour and with a smell of earth. The micro-organisms use more than one third of the
energy contained in the material, while the large, remaining quantity is released as heat.
This chapter describes the system assemblies forming part of the composting systems,
toilet stools, filters/separators and the collecting/composting units.
The parts may be assembled in batch composting systems or continuous composting
systems. A batch composting system consists of two or more containers or chambers. While
the toilet is used, one container or one chamber is filled. The material in the filled-up
unit is then composted without further supply of fresh faecal material. The composting
systems examined in this project are batch systems. Continuous systems may consist of
large one-chamber systems with flat or sloping bottoms. Fresh material is supplied
continuously at the top of the compost container. The amount depends on the frequency of
use and possibly on the supply of organic household waste and admixtures. A minor amount
of composted material will typically be removed from the bottom after 2-4 years for the
first time, and after that once a year.
Chapter 5: Description of the wastewater systems in the
project
The assemblies forming part of the two composting systems of the project are described.
One of them is a source diverting batch composting system with water flush, which is
installed at each household. It consists of a toilet with very small water flush (1-2
decilitres for urine and 0.5 litres for faeces) and of two "Kaggen" containers
with filters, used for drainage and composting respectively. In addition to this a compost
container – the "Quick Composter" – is used for the maturing stage.
The other composting system is the public source collecting batch compost toilet system
without flush, placed at the Skelsnæs Pavillonen. Here a toilet building includes two
separate rooms containing a source-collecting privy. When you use the toilet you sit on a
kind of cut-out wooden bench. In the room there is a bucket of sawdust to be used as an
admixture (for sprinkling after stools). By simple gravitation, faeces etc. will sink into
the underlying chamber. The system is designed for alternating batch running, using and
filling one chamber at a time. When one chamber is filled up, the substance can enter the
maturing stage without further supply of faeces and urine.
Chapter 6: Legislation
The chapter gives a short presentation of legislation relevant to the establishment of
a compost toilet, together with legislation related to the application of the compost as
manure. Finally, the legislation of other countries in this area is outlined.
Wastewater systems are regulated by the Environmental Protection Act as well as by the
Building Act. Plumbing must be performed according to the basic standards of waste pipe
installations (DS 432, 2000). Human residual products (urine and faeces) may be used for
agricultural purposes according to the sludge executive order (no. 49 of January 20th
2000 on the application of waste products for agricultural purposes). The possible
applications of urine and other humane residual products depend on how they are treated
(cf. guideline no. 5 of 1999 of the Danish Environmental Protection Agency on the
executive order on sewage permits etc., section 13.2.2).
Chapter 7: Experience gained from installation and running
A short presentation is given of the experience gained from the installation and
running of the compost toilet in the one-family house in Stubbekøbing and from the public
compost toilet at the Skelsnæs Pavillonen. In addition the users have indicated their
opinion on the system questionnaires
Experience from the running of the compost toilet system at Stubbekøbing
The toilet has posed great problems with the tilting device of the "Ecovip"
toilet and, thus, with the flushing of the faeces. The backward pressure of the spring was
not sufficiently strong to keep the system tight, and consequently the toilet was changed
into a DS toilet, which produces a larger flush (3-5 litres for faeces). The material
collected and composted in the "Kaggen", of which samples were taken for various
analyses, was collected from flushes with the "Ecovip". Apart from one single
choking, which could be mended by way of a cleaning wire or caustic soda, no problems with
the "DS" toilet were registered here. The family found that cleaning the faeces
unit of the "Ecovip" toilet was considerably more difficult than cleaning an
ordinary toilet. In return, they have been very satisfied with the "DS" toilet.
The filter in the first "Kaggen" was not properly installed; the filter bag
was placed too far down in the container. It would have been more convenient with more
suspension points than the four in the corners, and even better if an obvious method of
suspension encouraged correct fitting of the filter. In spite of this it was, however,
possible to supply faeces from the four persons having a high home frequency, for almost
13 months from the beginning of November 1998 to November the 26th 1999. The
assembled batch containing approx. 600 litres stayed untouched about one year, without
stirring, digging over or supply of admixtures. A shovel of compost containing worms was
added in June 2000.
In connection with the testing it was obvious that the compost substance was rather
compact during long periods of the composting process. After one year of composting in the
"Kaggen" the material was shovelled from the filter bag into the garden compost
unit, the "Quick Composter". The bottom 10-20 cm of the "Kaggen"
material is still not properly transformed; there are a lot of worms in the compost
material, however. Ten months later the material seems totally transformed. It looks like
sphagnum, and it smells good. The total reduction of volume during the two composting
phases is approx. 88%.
Experience from the running of the compost toilet system at the Skelsnæs
Pavillonen
The two toilets are used alternately. During mid-summer, the time when the number of
visitors peaks, they are used in terms, interchanging once a month and less frequently out
of season. The frequent changes are made because the chambers are filled up quickly.
During the "quiet periods" the material will collapse, and the composting
process will start. However, the collected material is primarily sawdust and paper. The
quantity of faeces seems to be small. The containers are emptied once a year, in late
autumn. The material is not entirely transformed, but because of its high content of
sawdust, the material does not appear repulsive. The material is buried as night soil. The
horizontal air shaft in the container is placed inconveniently. Material falling from the
toilet is caught by the shaft and prevented from further transportation, which means an
extra and unpleasant job for the service staff. Experience from Northern Jutland indicates
that the air shaft is dispensable.
In the summer of 2000, the users of the toilet at the Skelsnæs Pavillonen had the
opportunity to express their opinion about the toilet by filling in a questionnaire. All
the answers expressed great satisfaction with the system, which, in their opinion, had a
satisfactory standard when used as a "forest privy".
Chapter 8: Analysis results and comparison to other compost and manure material
Tests have been made frequently during the composting period, both from the
"Kaggen" and from the "Quick Composter". During the composting period
of just under two years the TS percentage rises moderately from 18.2 to 23.0. The humidity
percentages of 81.8 – 77.0 are far from the 60% which is considered ideal.
It appears from the analyses that considerable reductions of the total compost
substance and the constituents take place. The total reduction of organic material is 88%.
The results and the assessment of the volume indicate a considerable reduction of the
nutrient content. During the composting and maturing stages the original content of N is
reduced to 16%, P to 31%, and K to 42%. The output variables of the content of N and P
seem rather high compared to standard figures of excreted faeces.
The content of nutrients in the compost from Stubbekøbing is compared with the content
in the compost substances from other compost toilet systems as well as with the content in
sludge from household containers (sedimentation tanks), and in the faeces fraction
separated in connection with "Aquatron" separators.
Temperatures measured in the "Kaggen"
In the "Kaggen", temperatures have been measured during the composting
period, but not during supply and draining periods. The temperature development seems to
depend more on the exterior temperature conditions than on any increase of temperatures
caused by heat generating biological activity in the compost substance. The lowest
temperature recorded is 3° C, which indicates that there may have been periods of
insignificant micro-biological activity. Temperatures may have been even lower during the
period from January 16th to April 30th 2000, when temperatures were
not measured. The highest temperature, recorded in July 2000, is 21.4°C. The temperatures
measured are compared to the temperature development in the compost material of other
compost toilet systems.
Results from micro-biological analyses
During the composting and maturing stages five tests have been made, which have been
analysed for content of micro-organisms. The results prove that the number of thermo
tolerant coliforms has been reduced to 10 cfu/g (colony forming units) about one year
after the supply of faeces was stopped. At this time, the material still remains in the
"Kaggen". It has been neither ventilated, shovelled nor treated in any way. Ten
months later, after the material was transferred to the compost container, the next
analysis shows a content below the detection level (<10 cfu/g). Analyses of presumptive
E-coli show the same results. The number of enterococci is 12,000 cfu/g after approx. one
year, and 10 months later, at the next measuring, it is below the level of detection
(<100 cfu/g. No salmonella or campylobacter have been found in any of the tests. All
tests contain cryptosporidium parvum, but the amount is too small to quantify. The results
are compared with the content of selected micro-organisms in other compost substances
showing a similar large reduction.
Chapter 9: Experience gained from similar composting systems
This chapter presents the experience gained with the "Kaggen" in Sweden.
Moreover, experience from the County of Northern Jutland is shortly presented. Here, 20
compost toilets of the same type as the toilet at the Skelsnæs Pavillonen were installed.
Chapter 10: Discussion
On the basis of the experience gained from the use of the two composting systems, the
possibilities of optimizing both the components and the operation of the systems are
discussed. Furthermore, the quality of the compost material is discussed on the basis of
the content of nutrients and micro-organisms.
The capabilities of the two systems are assessed. The source-collecting toilet at the
Skelsnæs Pavillonen is, thus, most applicable at primitive camp sites, scout camps, at
recreational tourist sites, i.e. places where no modern conveniences can be expected.
Further, the system is very convenient even if the reduced volume of the system is used,
and the "compost" is buried as night soil.
The source diverting system of "Kaggen" is found an excellent alternative to
other composting systems and other low-technology sewage facilities, especially in the
countryside, where you find the greatest interest in using the compost for garden
purposes. There is, however, a need for analyses of the content of heavy metals and
organic xenobiotic substances, as well as for an assessment of the risk in connection with
the utilization of the compost product as manure, both with a view to the possible content
of these substances and to micro-organisms, including bacterial infectious matters.
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