1. SUMMARY
Significant seasonal fluctuation characterizes the amount of domestic sewage water around recreational areas in the temperate zone. The summer peak overloads the purification plants and destabilizes the steady state and its normal efficiency. To purify and utilize this surplus summer domestic sewage, we have developed a domestic sewage oxidation fish pond technology.
Herbivorous fish have a paramount role in this technology, since they constitute some 90-95 percent of the stocking population as well as that of the yield. They utilize natural food not utilized by common carp and, at the same time, favourably increase the efficiency of water reclamation.
The best result was achieved at a sewage water load of 100 m3/ha/day. With 100 m3/ha/day sewage water during the culturing period, 400-600 kg nitrogen and 80-120 kg phosphorus was introduced into the pond system.
In a properly operating system, the elimination of 80-90 percent of phosphorus and nitrogen load is warranted.
With the stocking structure described, 1.8-2 t/ha net output could be achieved at a 100 m3/ha/day sewage water load.
2. INTRODUCTION
As a consequence of intensive urbanization, our lakes and rivers are exposed to a gradually increasing pollution, urging the protection of a "healthy" aquatic environment.
Lake Balaton, with its unique natural endowments, provides pleasant sporting and recreational conditions for 10 000 national and international tourists. The water quality still meets the requirements of a resort, but a series of threatening signs calls the attention of authorities and experts to take measures for its improvement. Under our climatic conditions, the period between May and September is suitable for visiting the Lake area, during which time the amount of domestic sewage water increases three to five-fold. This summer peak overloads the conventional purification plants and destabilizes the steady state and its normal efficiency.
In the knowledge of biological features of this area, our aim was to establish artificial ecosystems (fish ponds), thereby utilizing and purifying the seasonally accumulating domestic sewage water.
Utilization of domestic sewage water dates back to the beginning of the 1900's. It was Hofer who applied it first in 1904 and 1911 (Falck, 1935; Kisskalt, et al, 1937). His work was followed by Demoll, whose experience was used when, in 1926, a fish pond system of 223 ha was established near Munich. This system worked properly even after 25 years, according to Kaufman (1958). Several European countries, such as Czechoslovakia (Pytlik, 1957), the Soviet Union (Unberg, Ljahnovics, 1965) and Poland (Németh, 1968) followed this example. Experience and data collected proved that notwithstanding some operational problems, the fish ponds worked fairly efficiently (Imhoff, 1956; Liebmann, 1960) .
In Hungary, the problem of domestic sewage water utilization in fish ponds had already emerged in 1914 (Halmi, 1914; Répássy, 1914), but no positive results were achieved. The problem, based on favourable experience abroad, came up again in 1958 (Gaál, Donászy, 1958) and launched publication of numerous papers (Woynárovich, 1959 and 1959a; Fóris, 1961; Holényi, 1962) which, besides discussing theoretical and practical questions, urged large scale experiments. In spite of all this, the attention was focused on the so-called domestic sewage oxidation fish ponds (Brinck, 1961; Uhlmann, 1962) since this management has no extra water requirement. We should note, however, that the two management systems cannot be sharply separated (Pytlik, 1957), since tench (Tinca vulgaris) and carp culturing can be managed in closed systems as well.
In spite of the controversy, trials were made by introducing domestic sewage water into the lakes. These attempts gave rise to the study of operational problems, such as formation of hydrogen sulphide (Vámos, 1959, 1961, 1967), algal bloom (Vámos, et al., 1963) and O2-CO2 circulation.
3. MATERIALS AND METHODS
The technology has six main units. The first is the pretreating block, where there is a wire netting system for primary filtering. The pollutants with finer structures are filtered through a sand trap, then the water is introduced into a depositing tank. The mud collected in the first unit is treated in the second one, in the pre- then in the post-putrefactor. The mud is then phase distributed; the liquid phase is chemically treated, and the solid part is pasteurized. The effluent water of the sterilization can be directly introduced into the ponds, while the mud is used in agriculture. The chemical treatment is done in the third unit in the following steps: preparation of chemicals, dosing, mixing. Thus, treated sewage water is retained and qualitatively tested in the fourth unit. The fifth unit, a sewage oxidation pond system is made up of three well defined blocks: fish ponds sewage water spraying block, and a monitor block for checking the purifying process.
3.1 Fish Ponds
The total area of this unit is 10.7 ha and is distributed between 12 ponds, 6 of which are 1.65 ha each and the other six are 0.18 ha each. For economic use of the area at disposal, the ponds are located in a fan shape. The average depth of the ponds is 1.0-1.3 m, the the bottoms are covered with peat. The above layout makes the individual treatment, filling and draining of the ponds, possible. The harvest is done from a pit moulded along the longitudinal axis of the ponds.
3.2 Sewage Water Spraying Block
The mechanically treated sewage water is pumped under high pressure to the sprinklers in the ponds. In each pond six sprinklers of Gemenc T type are used, both for aeration and spraying of sewage water. Sewage water spraying is generally done daily, in the morning hours. In the case of aeration, pond water is pumped into the sprinklers, instead of sewage water, thereby solving the problem of morning oxygen depletion in the ponds.
3.3 Monitor Block
This unit ensures smooth operation of the system as well as checking the purification procedure. There is a pump of low capacity in each pond to introduce the water to a testing laboratory. It is automated and works for 15 minutes, passing the water through the electrodes which are connected to recorders. There is an alarm unit in the monitor connected to the oxygen electrode and, if the concentration of soluble oxygen is lower than 3 mg/l, a sound gives alarm that aeration should be switched on.
Figure 1 shows the schematic layout of the technology. Units marked with an asterisk are not always necessary to build in.
In 1974, the first year of the five year research project, untreated ponds were used with a stocking density of 1 300-1 400 fish/ha. The technology was accomplished in 1975 when the spraying unit was put into operation. 50 m3/ha/day sewage water was sprayed in 1976 at a stocking rate of 3 000-5 000 fish/ha. In 1977, at the same stocking rate, we varied the sewage water loading, in doses of 75, 100, 150, 200 m3/ha/day, trying to find the optimal dose and applying, at the same time, the best stocking structure tried in 1976. In the last year of the project (1978) 100 m3/ha/day sewage water loading was applied at a stocking rate of 3 500 fish/ha. Cyprinid fish gave the best stocking material in a structure of 2-year old common carp, silver carp, grass carp and bighead, with 300-350 g individual weight.
Figure 1. Schematic layout of domestic sewage utilization in fish ponds
4. RESULTS
Our main problem was to find the dose of sewage water which does not cause any harm to fish, providing, at the same time, a proper grade or purification. Extreme doses of sewage water were used in 1975 at a uniform stocking structure. We found that, compared with the control, a load of 5 m3/ha does not significantly change the water quality and fish yield. At the highest loading of 250 m3/ha/day, however, a mass mortality occurred due to the early morning oxygen depletion in the ponds. The best result was achieved at a dose of 50 m3/ha/day, with a yield of 1.2 t/fish/ha.
In 1976 we optimized the stocking structure at a load of 50 m3/ha/day considering the feeding activity of the species, as well as the quality and quantity of natural nutrient sources of the pond. Considering the results of experiments carried out in 1976, we established that the rate of common carp could not be more than 10 percent in the stocking structure if we wanted to yield market size fish and properly purified water at the same time. Grass carp should have a share of 5-7 percent due to the huge mass of macrovegetation. The greatest problem was the rate of bighead which was the most aggressive species of the stocking structure. Its optimal rate was established as 22-25 percent. Silver carp grazing on zooplankton and phytoplankton had a great significance in the structure. The best purification grade and highest yield was achieved with the stocking structures, where the share of silver carp was 50-65 percent. The yields, as the function of stocking structure and number, ranged between 1.3-1.6 t/ha, which can, however, be enhanced by increasing sewage water loading, maintaining at the same time the water quality. In 1977 experiments were conducted using the experience of 1976, to find the optimal dose of sewage water loading.
The best result, 1.8-2.0 t/ha, was obtained at a water disposal of 100 m3/ha/day. The water quality obtained this way met all the requirements. In the case of sewage water loading higher than 100 m3/ha/day, the quality of water was significantly impaired and the yield decreased.
In 1978 we made final tests in the sewage water utilizing system, and found that the technology operated perfectly and fulfilled our expectations in every respect. Results of our five year research project are summarized in Figure 2.
4.1 The Most Important Parameters of the Technology
Optimal dose of sewage water disposed: 100 m3/ha/day
|
Which means |
400-600 kg nitrogen/year |
|
|
80-120 kg phosphorus/year |
|
Stocking structure |
|
|
|
Carp |
5-10% |
150 - 300 per ha |
|
Silver carp |
50-65% |
1 500 - 1 650 per ha |
|
Bighead |
22-30% |
750 - 900 per ha |
|
Grass carp |
8-10% |
240 - 300 per ha |
|
Total |
|
2 640 - 3 150 per ha |
Yield: 1.8-2.0 t/ha
Grade of purification; 80-90 percent
Qualitative parameters of purified water
|
BOI5 |
4-5 mg/l |
|
pH |
8.1-8.3 |
|
Soluble 0- |
8-10 mg/l |
|
Total nitrogen |
2-3 mg/l |
|
Total phosphorus |
0.7-1 mg/l |
|
ANA |
0.2-0.3 mg/l |
Figure 2. Diagrams of loading and stocking rates and yield in domestic sewage fish ponds
5. CONCLUSIONS
The purification technology of domestic sewage water in fish ponds is suitable for purifying and utilizing the summer surplus in recreational areas.
Applying the described method, domestic sewage water produced by 800-1 200 persons/ day can be purified in a 1 ha pond area.
This technology, besides the disposal and purification of sewage water, solves the problem of its utilization as well.
With the technology, 1.8-2.0 t/ha fish yield can be produced.
6. REFERENCES
Brinck, C.W., 1961, Operation and maintenance of sewage lagoons. Water Sewage Works, 1961: 466-8
Csanády, M.,1967, Szennyviziszap aerob lebontásának vizsgálata. Hidrol. Közl., 47(8):371-9
Donászy, E.,1958, Szennyvíz és halastó. Halászat, 2
Falck, T.,1935, Entwicklung der Abwasserreinigung in Fischteichen. Peg. Ing., 58
Fóris, Gy., 1961, Városi szennyvizek tisztítása és hasznosítása tógazgadásokban. Gödöllö. Kulturtechnikai jegyzet, ATE
Gaál, E.,1958, Városi szennyvizek tisztítása és hasznosítása halgazdaságokban. Viziterv Ert., 1
Halmi, Gy., 1914, Városi csatornaszennyvizek tisztítása halastavakban, Halászat, 15:147-9
Holényi, L.,1956, Szennyvízelhelyezes a Balaton környékén. Hidrol. Kozl., 42
Imhoff, K.,1956, Taschenbuch der Stadtenwasserung. Chapter 16. Oldenbourg, München, (cit. H. Liebmann (1960))
Kaufmann, J.,1958, Chemische und biologische Untersuchungen an den Abwasserfischteichen von München. Z. Angew. Zool.. 45:433-81
Kisskalt, K. and H. Ilzhöfer, 1958, Die Reinigung von Abwasser in Fischteichen. Arch. Hyg., 118:1-65
Liebmann, H.,1960, Biologic der Abwasserfischteiche. Biologic der Abwasserteiche. In Handbuch der Fischwasser und Abwasser-Biologie, by H. Liebmann. Jena, VEB Gustav Fischer Cerlag, Vol. 2:531-50
Németh, S.,1968, A halastavi trágyázás módszerei. Budapest. AGROINFORM, 90 p.
Pytlik, R.,1958, Oczyszczanie sciekow domowych oraz organichnych sciekow przemyslowych metoda statow akumulacyjnych i asymilacyjnych. Biul. P.A.N. Zaklad Biol. Statow Krakow., 11:132
Répássy, M.,1914, Halastó és szennyvíztisztítás. Halászat, 15:264-5
Uhlmann, D.,1962, Oxydationsgraben und Oxydationsteiche. Wiss. Ztsch. Karl-Marx-Univ. Leipzig, 11:187-99
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Vamos, R.,1961, H2S képzödés és a klimatikus tényezök szerepe a tömeges halpusztulásban. Hidrol. Közl.. 41(4):343-8
Vamos, R., J. Zsolt and M. Ribianszky, 1963, A vízvirágzás és a halpusztulás. Hidrol. Közl., 43(6):528-33
Woynárovich, E.,1959, Városi szennyvizek hasznosítása halgazdaságban. Halászat, 3:48
Woynárovich, E., 1959a, Létesíthetö -e szennyvíz-tógazdaság Magyarországon? Halászat, 4:64
