Incorporation of brewery activated-sludge single cell proteins (BSCP) in diets for Clarias gariepinus B. fingerlings

E. De Muylder, P. Van Damme, L.Vriens, R.Nihoul and F.Ollevier

In : AQUACULTURE - A BIOTECHNOLOGY IN PROGRESS, 1989.
N. De Pauw, E.Jaspers, H.Ackefors, N.Wilkins (Eds.)
European Aquaculture Society, Bredene, Belgium.

Abstract

Brewery activated-sludge single cell proteins (BSCP) was incorporated in high quality feeds for Clarias gariepinus B. fingerlings at levels of 4-22 %. BSCP incorporation was found to have a positive effect on the growth performance up to levels of 22 %. The optimum concentration of BSCP in feeds for Clarias gariepinus was 14 %. The problems associated with the use of activated sludge are discussed.

Keywords

Single cell proteins, Fish nutrition, Clarias gariepinus.

Introduction

An ever-increasing demand for protein sources of high nutritive value has stimulated the application of single cell proteins (SCP), yeasts, bacteria, and algae in animal feeds. The interest in industrial and municipal wastes as substrate for SCP production has increased concomitantly. Activated sludge single-cell protein (ASCP), a by-product obtained from the treatment of industrial and domestic wastes, has been proposed as a feed additive by various authors (Windell et al., 1974; Bays, 1977; Tacon and Ferns, 1978). Tacon (1979) argued, however, that microbial content, heavy metal, and other toxicological problems associated with the use of activated sludge could act against large-scale use as animal feed.
In earlier studies, Tacon (1979) and Anwar et al. (1982) already showed that activated sludge can be incorporated in the diets of Salmo gairdneri and Cyprinus carpio at levels of respectively 33 and 40 %, without important losses in either growth rate or feed conversion. The suitability of brewery-activated sludge (BSCP) as a feedstuff was reflected in extensive studies on poultry (Goto and Masuda, 1974; Ahn et al., 1979). Windell et al. (1974) indicated that BSCP can be added to trout diets up to levels of 10 %. Bays (1977) recommended the use of this brewery waste product as an important vitamin B12 source.
The aim of our experiment was to evaluate BSCP as a feed additive in diets for Clarias gariepinus fingerlings.

Material and methods

Fifteen 10 l aquaria were each stocked with 80 Clarias gariepinus fingerlings (mean initial weight = 1.72g). The temperature in all aquaria was maintained at 26 + 1oC by a constant inflow (+100 ml/min) of temperature controlled, aerated, and biologically purified waste-water from Breweries Artois. Samples of 30 fish were individually measured and weighed after 15 and 30 days. Feed conversion and growth rate were calculated for all fishes.
Five diets containing 0, 4, 8, 14 and 22 % of BSCP were formulated on an isonitrogenous base (Table 1 and 2), according to the nutritional requirements of Clarias gariepinus fingerlings (Machiels and Henken, 1985).

Table 1 : Composition of experimental feeds, formulated on an isonitrogenous basis (0.1 % vit C, 0.025 % BHA and 0.025 % Methionine were added to all experimental feeds). The numbers given are a percentage of the composition.
BSCP 0 4 8 14 22
Herringmeal 45 45 45 45 45
Malt sprouts 4 4 4 6 8
Malt dust 4 4 4 2 0
Spent grains 4 4 4 4 4
Torula yeast 13 14.5 14 12.3 7.5
Brewery yeast 22 16.5 13 9 4
Soybean oil 6 6 6 5.8 5.5
Starch 2 2 2 2 2


Table 2 : Chemical composition of the experimental feeds (in % of dry weight)
BSCP (%)Crude proteins (%)Fat content (%)Energy content (KJ/g)
0 48.88 9.51 17.17
4 49.39 9.58 16.99
8 49.42 9.58 16.80
14 49.61 9.62 16.55
22 48.52 9.62 15,80

The five different treatments were distributed at random in three replicates over 15 aquaria. A feeding rate of 6 % of the predicted body weight, which was calculated daily according to an expected growth rate, was maintained. The dried BSCP, of which the composition is given in Table 3, was obtained from the waste-water treatment plant of Breweries Artois.

Table 3 : Proximate analysis of the conventional and the biomass brewery-activated sludge obtained from the water treatment plant of Breweries Artois (values are expressed on a moisture free basis).
BSCP
ConventionalBiomass Production
Ash content (%)34.35 26.64
Crude Proteins (%)25.83 45.20
Fat content (%)2.44 3.02
Fibre content (%)1.14 1.16
Energy content (kJ/g)14.01 16.14

The diets were pelleted, sized, and fed by hand to the randomly-assigned replicates.
During this experimentit was found that both growth rate and feed conversion show a quadratic performance in relation to the incorporated level of BSCP in the diets. To determine the optimal level an analysis with the GLM SAS-procedure was carried out, using the following model :
yi = c + b1 x + b2x2 + b3p +ej (1)
in whichy = growth rate, respectively feed conversion;
c =intercept;
x =level of BSCP in the diet (%);
p =period (p=0 for period 1, day 0-14, p=1 for period 2 day 15-30);
b1, b2, b3 =regression coefficients;
ej =error term.
The values of b1 and b2 are used to calculate the optimum level of BSCP incorporation in the diet (r) :
- b1
r = ------ (2)
2 b2

Results

Table 4 : Growth rate and feed conversion of Clarias gariepinus, recieving diets with different incorporation levels of BSCP.
 Weight (g)Daily growth rate (%)Feed conversion)
BSCP (%) DaysDays
  Initial Final 0-14 15-30 0-14 15-30
0 1.62a 8.92a 6.09a 5.93a 1.19a 2.55a
4 1.71a 14.87b 7.48b 9.52b 0.85b 1.20b
8 1.77a 14.00b 7.22ab 8.18b 0.90b 1.05b
14 1.61a 15.68b 7.35b 9.93b 0.78b 0.96b
22 1.73a 15.37b 7.57b 8.61b 0.79b 1.09b
a, b : Means with the same superscripts are not significantly different within each column. (Duncan's multiple range test, P<0.05).

Daily growth rate and feed conversion for days 0-14 and days15-30 are shown in Table 4 and in figures 1 and 2. Both growth rate and feed conversion improve significantly for the groups fed with diets containing BSCP, compared with the control group. The incorporation of BSCP in the diet which gives the highest growth rate and lowest feed conversion was determined to be 14 %, using formula (1) and (2). Both the regression coefficients b1 and b2 were significantly different from 0 (P 0.05), which confirms the hypothesis that growth rate and feed conversion have a quadratic course in relation to the level of BSCP in the diet.

Figure 1. Daily growth rate in relation to the level of BSCP in the feeds for the 2 periods : observed (points) and estimated function (lines).
Figure 1
Figure 2. Feed conversion in relation to the level of BSCP in the feeds for the 2 periods : observed (points) and estimated function (lines).
Figure 2

Discussion

It is clear that also for Clarias gariepinus BSCP can succesfully be added to high-quality diets, which contain high levels of fish meal and torula yeast, replacing torula yeast and brewery yeast on an isonitrogenous base. The diets containing BSCP are found to give better results than the diets without BSCP. Several authors assumed that BSCP contains important qualitative and quantitative nutrients. Bays (1977) and Pillay et al. (1967) already mentioned that appreciable quantities of vitamins of the B group, in particular vit. B12, are present in ASCP. Besides, the BSCP has a high mineral content, with a large range of trace elements (Table V).

Table V. Trace elements of BSCP and ASCP (values are expressed as ppm by dry weight)
BSCPASCP
Metal Artois Bays (1977) Tacon (1978)
Fe 7100 - 9000-16500
Cd 6 - -
Cu 420 110 150-370
Ni 150 5 10-23
Pb 21 7 60-120
Zn 365 200 460-860
Cr 128 9 12-20
Hg 0 0.1 -
As 3.2 - -

Because of the more constant composition of the waste water there is a greater possibility to control activated sludge from food processing effluents compared to such activated sludge obtained from municipal waste waters. In activated sludge from sewage, Tacon and Ferns (1978) found high levels and considerable fluctuations for some heavy metals. In biological sludges emanating from the food processing industry such problems are unlikely to occur. If present, they can be avoided by changing the process.
The relatively low protein and energy content of the used BSCP (Table III) causes some problems in formulating diets with high protein and energy levels and excludes incorporation of higher levels. However, the 'biomass production' approach aims at maximizing the production of proteins in the BSCP. In this approach, a higher loading obtained by application of a shorter retention time of the waste water, results in a higher biomass production. Adding a nitrogen source to the waste water results in production of a biomass with a higher protein and energy content (Table III)(Vriens et al., 1983). However, only an effective valorization of this BSCP can compensate the higher cost of this biomass production process.
Orme and Lemm (1973) already mentioned the importance of heat-drying to disinfect the ASCP. This treatment, however costly, offers also other advantages because it gives the activated sludge a form in which it can be stocked and processed more easily.
This preliminary study shows that BSCP can be used in levels up to 22 % of the diet without apparent losses in either growth rate and feed conversion. The optimum level of the BSCP in the diet was determined to be 14 %.
Further investigations have to focus on two major problems. First, more experimental research has to be done to determine the safety of using BSCP and secondly, the economical feasibility to use a biomass production process to improve the BSCP qualities have to be evaluated. The use of BSCP as an animal feed supplement would eliminate a waste management problem as well as create a new product for the food processing industry. High treatment costs are more likely to be a limiting factor than problems associated with the technology of processing and application of the BSCP.

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