Anaerobic treatment of protein, lipid and carbohydrate containing wastewaters using the EGSB technology

Industries such as margarine, meat packing, dairy, slaughterhouse, edible oil (palm and olive oil) generate large amount of effluents. Strict environment laws in numerous countries has forced these agro-industries to apply suitable wastewater treatment in order to reduce the organic pollution load before discharging the effluents to receiving waters. Anaerobic treatment comprises a very attractive and suitable method for these industries, where the effluents frequently are composed of mixtures of proteins, lipids and carbohydrates. The research described in this thesis deals with the feasibility of anaerobic treatment for complex types of wastewaters, e.g. containing mixtures of lipids, proteins, and carbohydrates. In the research particular emphasis was afforded to the application of Expanded Granular Sludge Bed (EGSB) reactors, because results obtained in earlier research indicated that the EGSB reactor-system might represent special promise for lipid containing wastewaters.

Chapter 1 provides a brief literature survey of relevant reports dealing with the production of complex industrial wastewaters and with information about the feasibility of anaerobic treatment systems like anaerobic sludge bed reactors, viz. the well known UASB-system and the more recently introduced EGSB-reactor.

Chapter 2 deals with investigations concerning the degradation of a milk-fat emulsion using a closed circuit with an EGSB reactor as treatment system. The results of the experiment show that 70 % of the lipids were adsorbed on the granular sludge. This adsorbed fraction remained greatly non-degraded; as a matter of fact only biodegradation was found for the colloidal fraction, although the process proceeded very slowly, which mainly could be due to the very slow rate of hydrolysis, viz. a value of the hydrolysis rate k _{h ,} of 0.01 d ^-1was assessed. The main mechanism prevailing in the lipid removal in an EGSB-system comprises a sorption process.

Chapter 3 deals with investigations conducted with an expanded granular sludge bed (EGSB) reactor equipped with a sieve drum as gas-liquid-solid separator device (GLS) to prevent the wash-out of buoying sludge. Two sieve drum designs were evaluated in experiments conducted with complex synthetic wastewaters composed of mixtures of carbohydrate, protein and lipids. One of these devices was capable to retain floating granular sludge efficiently and without damaging the granular sludge structure. The results of this experiment also revealed that 85 % of effluent leaving the reactor consisted of 'soluble' type of pollutants. The hydrolysis and acidification of this fraction was found to proceed very slowly. Moreover a peculiar phenomenon manifested, i.e. drops in the concentration of non-acidified soluble COD (NAS) in the effluent coincided with an increase in the amount of colloidal COD and vice versa. Results presented of batch biodegradability assays with different types of proteins, e.g. originating from potato, corn, milk, egg, gelatin and bovine. The results revealed that the deamination generally proceeds well, but the conversion of the proteins into methane-COD looks rather unsatisfactory.

The investigations in Chapter 4 were addressed to the application of the EGSB technology to complex synthetic wastewater composed of carbohydrates, beer, proteins like gelatin and a milk-fat lipid emulsion. The results show that the organic pollutants originating from or present in beer and gelatin were well removed at a high COD removal efficiency (90-95 %), and at a satisfactory COD-conversion efficiency to methane, i.e. for 85 %, at imposed OLR's up to 12 g COD/l d. The deamination of gelatin amounted to 86-89 %. Lipids, applied in a concentration of 0.260 g COD/l, did not detrimentally affect the reactor performance. However, on the other hand the degradation of lipids did not proceed satisfactorily.

Chapter 5 presents results of research dealing with the applicability of the EGSB reactor to wastewaters composed of mixtures of gelatin and sucrose using non-adapted granular sludge and in presence/absence of macro-nutrients. The results show that the degradation (i.e. the deamination) of gelatin reaches 70-90 % at space loads up to 7 g COD/l.d , but once again the acidification remained poor and the conversion to methane amounted only to 65 %. Nevertheless a high COD removal efficiency was found with a figure in the range 85-90 %, indicating that a certain fraction of the gelatin or its intermediates have become sorbed to the sludge surface or precipitated in the reactor.

Addition of sucrose to the experimental feed solution resulted in a slight improvement of its deamination, but also in further decline in the fermentation process. After addition of nutrients to the feed solution, viz. simultaneously with gelatin and sucrose in the feed storage vessel, the pre-acidification of both these substrates improved. But when gelatin and sucrose were introduced via separate lines in the reactor, the fermentation of gelatin dropped sharply. From these observations it can be concluded that apparently sucrose seriously depresses the fermentation of gelatin.

Chapter 6 summarizes the results of the experiments, and the scientific relevant aspects are highlighted and discussed. Moreover, based on the insights obtained, some recommendations for the operation of an EGSB-system have been provided.