I. THE USE OF DOMESTIC WASTE WATER FOR FISH CULTURE IN POLAND

Abstract

In Poland detailed investigation of fish culture in biologically treated waste water proved that common carp can be cultivated all the year in undiluted effluents from an activated sludge plant. It is recommended to use two-year-old carp since carp fry are adversely affected by retention times shorter than ten days and low oxygen concentration. These larger fish also have better treatment effect on the effluents. Fish yields over 1 000 kg/ ha were obtained without artificial feeding. Short notes are given on places where wastes of different types are utilized for fish culture.

Résumé

En Pologne, des investigations détaillées sur la culture du poisson dans des eaux résiduaires biologiquement traitées ont prouvé qu'il est possible de cultiver la carpe toute l'année dans des rejets sans dilution provenant d'un processus de boue activée. Il est recommendable d'utiliser des carpes de deux ans parce que les alevins sont inversement affectés par une période de rétention inférieure à dix jours. Le poisson adulte a, en outre, un meilleur effet de traitement sur les rejets. On a obtenu des rendements de poisson de plus de 1 000 kg/ha sans alimentation artificielle. De brèves notes sont aussi données sur quelques endroits où l'on utilise des rejets différents pour la pisciculture.

1. INTRODUCTION

Water pollution by domestic waste water is creating problems at an increasing rate. The increasing population and the even more rapid urbanization makes the problem more pronounced, not only in the developed nations but all over the world. Especially in the developing countries the problem is difficult to handle due to several circumstances: shortage of capital, shortage of technical know-how, and inadequate administration. The shortage of proteins in these countries is well-known. It is therefore natural that FAO should take a vivid interest in possibilities to grow fish in domestic waste water in order both to control water pollution and obtain cheap proteins.

Most of the literature on this subject comes from German sources (Allen, 1969), but not very much is known on the activities in the socialist countries, partly because of difficulties in obtaining translated literature.

2. FISH CULTURE IN BIOLOGICALLY TREATED DOMESTIC WASTE WATER

Extensive investigations were carried out by Wolny (1962, 1967) at the sewage treatment plant at Kielce (Fig. 1) in southern Poland during the period 1958 to 1961. The sewage from the town is treated by the activated sludge method (without clorination) and the aim of the investigation was to determine if fish could be reared in the undiluted effluents over the whole year. In the literature it has been stated that fish culture in sewage is only possible with extensive dilution which would constitute a severe limitation of the method.

Investigations were carried out in five ponds of which two were stocked with common carp (Cyprinus carpio) and two were left unstocked as control ponds. Parallel investigations were carried out in ponds with and without overflow. The deepest pond was used as a wintering pond (Table 1). The effluent from the treatment plant had a composition normal for biologically treated domestic effluents (the phosphate content was lower than that usually found after the introduction of washing agents rich in phosphate).

Fig. 1 Kielce sewage treatment plant and fish ponds. Photo: P. Wolny

Table 1

The characteristics of experimental ponds (from Wolny)

Explanations: z: stocked pond;
k: control pond;
p: pond with overflow;
bp: stagnant pond;
figures: retention time (days)

Development of aquatic plants was very effectively prevented by the fish in the stagnant ponds only. The reason was that when feeding on the bottom fishes stir the sediments thereby decreasing transparency and consequently also growth of aquatic plants. In flowing water the effect is, however, less pronounced as the suspended sediments are continuously removed.

Development of phytoplankton was influenced by the fish and green algae with short development cycle (Chlorella and Scenedesmus) were dominant in the stocked ponds throughout the vegetation season, whereas in the unstocked ponds other algae forms dominated (Oscillatoria, Scenedesmus, Pediastrum).

The dissolved oxygen was higher in stocked than in unstocked ponds due to the species composition of phytoplankton and the effect was more marked in stagnant ponds. The oxygen content never fell under 3 mg/l at which level the crucian carp stops feeding. The development of bottom fauna was favoured by stocking. Both numbers of individuals and weight of bottom fauna per m² were greater in the stocked ponds. The fish also increase the bottom surface by ca 35 percent by continuously “digging” in the bottom. In ponds with overflow it was found that the bottom fauna was eaten to a less extent by fish. The oxygen content was lower at the bottom in these ponds and in order to utilize the bottom fauna such ponds should be stocked not with fish fry but with two-year-old fish which have lower oxygen requirements. The sewage was rich in fat and in autumn the carp was feeding also on floating fat particles. The good food conditions resulted in lower weight losses during winter and also in fish flesh with higher content of fat and protein as compared to values obtained at the fish ponds at abienieo with fish of the same age reared in unpolluted water (Table 2).

Table 2

The content of fat, protein and dry weight in the body of carp fry on 9 April 1961 after wintering (percent) [from Wolny]

Winter pond No.	Food of fry during growth	Water supply	Average weight per specimen g.	Fat	Protein	Dry weight
3	natural	purified sewage	11.1	4.1	12.7	21.4
13	natural	river (abieniec)	12.3	1.4	9.1	12.4
3	ground barley	river (abieniec)	48.1	5.9	11.9	21.0

The increase in weight was much higher than what is usually obtained without additional feeding in Polish carp ponds. For fry the increase in weight in stagnant ponds was two to three times higher than in the ponds at abieniec. In ponds with overflow, however, the increase was lower than in common ponds. For two-year-old fish the increase was six to eight times that in common ponds without additional feeding and there was no significant difference between ponds with or without overflow. The highest production obtained amounted to 1 317 kg/ha, the highest yield ever obtained in Poland.

The mortality of the larger fish and fish fry was not different from normal ponds provided the retention time for the ponds with fry was not less than ten days. There was also no difference in occurrence of parasites or diseases as compared with normal ponds. Carps were kept over the winter for five months in one deep stagnant pond filled with treated sewage. No abnormal mortality occurred although the oxygen content in December and January was somewhat lower than in common ponds (Table 3). No tainting of fish flesh was noticed, nor did any public health effects appear.

Table 3

The average oxygen content in mg per 1 and percent oxygen saturation in water in winter ponds - 1958/59 and 1960/61 [from Wolny]

The following conclusions were drawn from the investigation:

Successful carp culture can be obtained the whole year in undiluted biologically treated domestic waste water.

Conditions for fish culture are better in stagnant ponds than in ponds with overflow; ponds with overflow should be stocked with two-year-old fish or not have less than ten days retention time.

Stocking with fish provided additional treatment of the waste water and larger sized fish have better effect on reduction of organic matter than fish fry. A 50 percent reduction in bacteria was observed.

Optimal rate of stocking with fish is, because of the good food supply, higher than in normal ponds and was, in Kielce, found to be 25 000–35 000 fry or 2 500–3 000 two-year-old fish per ha.

3. OTHER EXPERIENCES WITH FISH CULTURE IN DOMESTIC WASTE WATER

The investigation undertaken at Kielce by Wolny seems to be the only scientific investigation in this field in Poland. There are, however, other places where sewage and organic wastes are being utilized for fish culture and the following were mentioned.

At Legnica untreated domestic waste water is spread over grass fields and from there it is drained into fish ponds covering 50 ha. This practice has been going on for 20 years and the fish production is 500–700 kg/ha without additional feeding.

At Zaglówek untreated domestic waste water is led into a series of ponds covering 55 ha. The first pond does not hold fish. With supplemental feeding a production of 3 000 kg/ha has been obtained in some ponds.

An attempt to grow fish in domestic waste water mixed with 65 percent waste from a metal factory at Czestochowa was not succesful because of high phenol content.

A limited investigation was undertaken of fish culture in biologically treated dairy wastes at Leszno. The ponds were too shallow for continuous fish culture but still a production of 800 kg/ha was obtained in one vegetation season. This experiment may be repeated and a similar investigation at Wilga has been discussed.

4. ADMINISTRATIVE VIEWS

The Polish authorities dealing with water pollution problems do recognize the beneficial effects from utilizing domestic waste water as well as other wastes for fish culture or in agriculture. Their first priority for the years 1971–1975 is, however, to build 1 000 new treatment plants and new water reservoirs with a total capacity of 5 000 million m³ and over 9 000 million złoty (ca $300 million) will be invested. Only after 1975 will the authorities actively propagate the use of fish culture in wastes in order to obtain additional treatment and increased protein production.

5. CONCLUSIONS

From the Polish investigation it is clear that fish culture in domestic waste water can give very high fish yields at low cost. It is also clear that with biologically treated sewage fish culture can be undertaken on a continuous basis. In order to convince engineers and authorities of the suitability of the method, closer investigations should be undertaken of the treatment effect of the fish ponds on the final effluents.

With regard to some developing countries the method would be of great value where due to favourable climatic conditions, it might be possible to cultivate fish in domestic sewage without pretreatment or dilution. Dr. Wolny especially pointed out that care should be taken to stock larger sized fish with low oxygen requirements in the first pond in a lagoon system because thereby both the efficiency of the treatment process and the fish yield would be increased.

Where domestic wastes are mixed with industrial effluents fish culture in the treated effluents can be successful only if there is satisfactory control of the industrial discharges. Fish culture can then give the necessary motivation to bring forward the needed pretreatment.

On the other hand, on many occasions there has been mentioned the public health implications of eating fish grown in domestic waste water. This objection is usually raised by some scientists from highly industrialized countries and are based more on emotion than practical experience. It is, of course, not proposed that the public health aspect should be ignored; on the contrary, this aspect should be further investigated and the risk be weighed against the advantage.

6. REFERENCES

Allen, G.H., 1969 A preliminary bibliography on the utilization of sewage in fish culture. FAO Fish.Circ., 308

Wolny, P., 1962 Prydatność oczyszczonych ścieków miejskich do hodowli ryb. (The use of purified town sewage for fish rearing). Polish with English and Russian summaries. Roczniki Nauk Rolniczych Seria B Zootechniczna, Warszawa, TOM 81, B (2):231–49

Wolny, P., 1967 Fertilization of warm water fish ponds in Europe. Proceedings of the FAO World Symposium on Warm-water Pond Fish Culture, Rome, 18–25 May 1966. FAO Fish.Rep. (44) Vol. 3, pp. 64–81

A - holding reservoir; 8.4 ha, 80 000 m³

B - fish pond 1; 10.8 ha

C - fish pond 2; 7.9 ha

Fig.2 Treatment of sugar factory wastes, Gołysz