5. New Technology
Although simple process changes, and cheap modifications can be used to make dramatic
changes in pollution loads, this does not mean that there is no need for new technology, and the
solutions that new technology provides. Below are two new technologies in wastewater
treatment.
5.1 - The Urine-separating toilet
One approach to making wastewater managemnent more sustainable is the urine-separating
toilet, which is rapidly gaining popularity in the Scandanavian countries (particularly Sweden).
The toilet has been installed in a number of Sweden’s “ecological villages” and is proving have
beneficial effects in reducing water use, and efficient recycling of nutrients to agriculture.
The urine-searating toilet appears similar to a convential toilet, but the bowl is seperated into two
sections by a central wall. The front bowl is intended for the collection of urine; the rear bowl for
the construction of solid waste. Each bowl can be flushed independently.
Figure 5 - The urine separating toilet
The effects of the urine-separating toilet on water consumption are dramatic. At one eco-village
in Sweden, total water used in toilets dropped from 195 litres/person/day (Swedish average) to
just 98 litres/person/day. At a second eco-village, Understen, total water used in flushing the
front (urine-collecting) bowl averaged just 0.4 litres/person/day. The 0.4 litres of flushwater
contributed to a total urine-solution collection of 1.4 litres/person/day.
In both Swedish eco-villages, the separated urine is stored in tanks, for periods of up to eight
months at a time. When the tanks are full (or fertilizer is required for crops) urine is removed,
and sprayed onto fields. Urine is a particularly good source of ammonia/amonium. Urea in urine
rapidly dissociates in ammonia/ammonium, which is present at concentrations of 3.635 g/l. In
addition, urine is much much lower in contaminants (such as heavy metals) than commercial
fertilizers. Figure 6 (below) compares levels of contaminants in urine (when used to give 100kg
Nitrogen/hectare of agriculturall land)with allowable levels in Sweden for the year 2000 (limits
which will be among the lowest in Europe.
Figure 6 - Urine as a fertilizer
Another of advantage in using urine as a fertilizer, is that much of the urine is available to plants
directly as ammonia/ammonium. This is not the case with mineral fertilizers.
The separation of urine from solid waste, allows the solid waste to treated usefully also. At
Björsbyn eco-village in Swedne, the solid waste passes through a septic tank and into a sludge
composter. Sludge is removed from the composter, dried, frozen and composted further. After
this treatment, it is then suitable for use on fields as fertilizer and as a soil enricher.
5.2 “New Generation” Reed Bed Filters in France
[This section taken from the report on Constructed Wetlands]
Since the 1980s, French researchers have investigating the use of Reed Bed Filters (RBFs) to treat
sewage from small communities. Currently, there are 15 RBF systems in France, each treating
waste from populations from 100-250 people (p.e) each. The systems are capable of receiving
raw sewage (usually screened to < 2cm). They typically comprise several Type A (primary
treatment, 1.15 m2/p.e) and 2 Type B (secondary treatment, 1.05m2/p.e) filters. Variant systems
sometimes use 1 Type C (horizontal) filter instead of a second Type B.
Figure 7 - New Generation Reed Beds
Typically there are a number of Type A filters. Each is loaded with waste for 3 to 4 days, before
being rested for 6 to 8 days. These rest periods are critical to the functioning of the system; they
allow mineralisation of Total Suspended Solids and maintain aerobic conditions in the gravel and
rhizomes.
After 15 months of operation a detailed examination of the Montromant plant was undertaken
over 48 hours. During the period of testing, temperatures varied from -8.5°C to +6.5°C . The
results of the experiment showed the system to be highly effective at improving water quality
(see Table 2)
Table1 - Performance of New Generation Reed Bed Systems (conc. in mg/l)
Total COD
d
COD
BOD5
TSS
TP
PPO4
TKN
Raw Sewage
495
190
215
225
8.5
6.4
42.8
Filter A outflow
92
70
0
18
5.8
5.3
19.6
Final Outflow
58
40
16
12
5.6
5.1
10.1
Removal (%)
87.5
80
92.5
94.5
40
28
76
The application of raw waste to the A-type filters was shown to result in sludge accumulation of
1.5 cm/year, however this accumulation has not been shown to inhibit breakdown of waste, even
at sludge-heights of 15 cm. Nevertheless, accumulation of such sludge should be allowed for in
design of tank height (if it is not to be removed manually at a later stage).
6. Conclusions
The field of wastewater treatment, and its sustainability is a large and complex one. In this
report, spome of the key areas of interest have been identified and discussed. This discussion is
at a broad level, and more technical detail is available about most aspects covered. Please feel
free to contact me by email for more information.