Fermentation assisted byproduct recovery in the palm oil industry

Fermentation assisted byproduct recovery in the palm oil industry

Agricultural Wastes 6 (1983) 31~ 3 Fermentation Assisted Byproduct Recovery in the Palm Oil Industry W. R. Stanton Private Consultant, Petaling PO Bo...

1MB Sizes 0 Downloads 77 Views

Agricultural Wastes 6 (1983) 31~ 3

Fermentation Assisted Byproduct Recovery in the Palm Oil Industry W. R. Stanton Private Consultant, Petaling PO Box 46, Kuala Lumpur, Malaysia

ABSTRACT The production of palm oil from Elaeis guineensis is a leading natural product industry m Malaysia, giving rise to a number of residues, including a rich, fruity liquor from the pulp. The liquor, of which 7.- 10 million tonnes a year are currently produced, has some 6 % organic solids, including O.7-1.0 ol, or more of o i l which physical processing has failed to extract. Present anaerobic digestion processes exploit only the energy and fertiliser value. Methods are described in this paperJbr thermophilic, microbially assisted digestion for component separation and recovery, exploiting the widely used techniques for fruit juice extraction invoh'ing enzymic breakdown of starch, pectin and other cell components. Anaerobiosis and acidogenesis help protect and release residual oil, concomitantly preserving the solids against rancidity and spoilage by ensilage. The separated wet solids are nutritive (17% protein on dry matter), biologically safe and attractive to livestock. Downstream use of the liquor is aided by the thermophilic digestion.

INTRODUCTION During the last decade a number of events have arisen which have forced the palm oil industry to reconsider the production and processing methods employed. This contrasts with the very slow rate of change which occurred in the previous fifty years, during which period, although there had been engineering modifications, the basic principle of palm oil extraction had changed very little from that evolved at the centre of 31 Agricultural Wastes 0141-4607/83i0006-0031,;$03.00 ,(" Applied Science Publishers Ltd. England, 1983. Printed in Great Britain

32

w. R. Stanton

domestication of the crop, Equatorial West Africa. These events are as follows. Land hunger: The edge-of-the-petri dish effect The moist equatorial lands of the world contain only a small fraction of the total agricultural land available in the world as a whole, but that land has some of the highest biomass-producing capacities. Demand for land for equatorial agriculture has been met, until quite recently, by cutting down virgin equatorial rain-forest (Myers, 1978). This plunder of the forest has sustained the steady growth of the rubber, palm oil, other tree, and annual crop industries, with little thought to the consequences of the impact on the global environment brought about by the destruction of the equatorial deep-tree cover, or even of the local environmental effects occurring adjacent to the clearing. With proper land management, permanent tree-crop agriculture has a relatively low environmental impact, compared with destruction of forest for rangeland, in terms of climatic change, soil destruction (Fig. 1) and soil runoff (Sagan et al., 1979). However, the conversion has reluctantly been accepted as a necessary evil of development, because of the relative ease of processing the biomass derived from a monoculture, in comparison with that which might be derived from the mixed equatorial-forest standing crop. Cost of pollution Nevertheless, in spite of careful management, serious pollution may be created from the clearing, plantation agronomy and the processing of the harvest of these tree-crops, the effect of which is now being felt by equatorial communities. Action is therefore being taken by government in the form of gazetting official pollution control regulations (Maheswaran & Singam, 1977) (Table 1). Land hunger has, however, had the economic effect of increasing the capital required for the fixed asset, the land for the plantations. A rise in the cost of production can only partially be averted by increasing the nett yield of useful prime product, since the cost of other inputs has also escalated, particularly due to the escalation of oil prices. In practice, the world market price of palm oil, the concern of this paper, has fallen. Thus, the palm oil industry has been forced to consider more effective use of the total biomass harvested, not just the production and marketing of the vegetable oil.

Byproduct recovery in palm oil mills

33

Fig. I. Gullyerosion induced by land clearing for development. Photo taken by the author from the Botanic Garden of the Universityof Malaya showing3.5 m gullyerosion caused in 6 months on 20 ° slope. Several authors have reviewed (Singh & Ng, 1968; Olie & Tjeng, 1970: Stanton, 1974; Collier & Chick, 1977; Davis, 1978; Sutanto, 1979) possible methods of utilising all the products of the palm fruit bunch, the component harvested, from which is extracted the palm oil. This paper is concerned with biotechnological methods for processing the fruit bunch, with special reference to the application of the properties of thermophilic fermentation processes in relation to product recovery.

Processing of the palm fruit bunch The present method of processing the palm fruit bunch, universally adopted by the industry, is depicted in Fig. 2.

34

W . R . Stanton TABLE I Parameter Limits for Watercourse Discharge Parameters

Limits accordh~g to periods o f discharge 1-7-197830-6-1979

1-7-197930-6-1980

1-7-1980 30-6-1981

5 000

2 000

1 000

10 000 4 000 I 200 150 25 200 5.0-9-0 45

4 000 2 500 800 100 15 100 5.0-9.0 45

2 000 2 000 600 75 15 75 5.0-9.0 45

Biochemical Oxygen Demand 3-day, 30 °C (mg litre - t) Chemical Oxygen Demand (mg litre - ~) Total Solids (mg litre- ~) Suspended Solids (mg iitre- 1) Oil and grease (mg litre - ~) Ammoniacal nitrogen (mg litre - ~) Total nitrogen (mg litre- ~) pH Temperature (°C)

1-7-198130-6-1982

500 1 000 1 500 400 50 10 50 5-0-9.0 45

From Maheswaran & Singam (1977).

All the methods currently in use employ handcutting of the bunch. This bunch, weighing about 20 kg, is then allowed to fall to the ground, or at best into a net, resulting in a variable amount of bruising, and the adhesion of soil and extraneous vegetable matter to the bunch is aided by the spikiness of the inflorescence organs. From the point of view of maximum yield of oil per bunch, the bunches are harvested prematurely, because, at this stage, some of the fruits being unripe, only a small number fall free of the bunch prior to, or during, harvest; the unfavourable economics of fruit gathering militate increasingly against recovering the individual fallen fruitlets. Palm shaking to cause loose fruit to fall onto a mat and the converse, hormonal retention of fruitlets in the bunch, have been tried but not adopted. During the final stage of ripening some fruitcell-enzyme induced breakdown of the oil occurs so that the Free Fatty Acid:(FFA) level is liable to rise, but this ripening effect is only one of the causes of high FFA, as it is commonly termed, in the palm oil at the point where it is received by the consumer industry. Free acid is removed during refining and, for many purposes, the Free Fatty Acid is itself a valuable commodity. The greater ripeness means that the oil droplets are more freely dispersed in the fruit mesocarp cells and the mechanical

Byproduct recovery in palm oil mills

35

10. 000 KG5 FRUIT BUNCHES

EI:B.

-

I

Reception

J

!

Steriliser

j

---"-EVAPORATION 1.055 tl*l,

(I,09/. KG5 WATER) ( 6 KG5 OIL )

~--- COND(:NSATE TO DRAIN

8.900 KGS BUNCI'IES

i 5tripper

1 1 O~estor

]-

2,100 KGS EMPTY BUNCHES INCLUDING 49 KGr, OIL - - - - a D -

T0 INCINERATOR

6,800 KG5 STERILISED FRUITI T RASH

Press

Clorif ication

]

•I

i

2,000 KGS OIL

Storage

Fig. 2.

--

J

]

3,055 KGS PRESS CAKE

765KGS OILY SLUDCAE|$ASKG$ OIL ~ - ~3o KGS Sot©. / % [3745 KGS SLLJOG~ (37S KGS OiL, 3145 KGS WATER) ~,ANo215 KGS ~ON (~LY S O U P S / I

J

[5~udgeCentrifuge ] ~

],000 KGS SLUDG~ TO DRNN(30 RGS 0~., 210 KGS SOLIDS AND 2,/60 KGS WATER)

Materials balance in the processing of lO000kg fresh fruit bunches.

disintegration of the fruit, to release the oil droplets, is aided by the ripening process (Fig. 3). At the factory the fruit bunches are held in open bins for up to 2 days; sometimes longer during the holiday periods. Preferably, retention is for a much shorter period, since further biodeterioration is liable to take place during storage. To extract the oil the whole bunches are sterilised in 1.5-2.5 ton skips at 140°C for 75-90min (total cycle time) before the individual fruits are mechanically stripped off. The sterilisation arrests all enzymic and microbial deterioration, although the mechanical methods of stripping the fruit from the bunch result in some oil being transferred

36

W. R. Stanton

LONGITUDINAL

TRANSVERSE

~ONTENTS BY WEIGHTOF PERICAR~SHELLAND KERNEL MACROCARYA P 3 0 - 5 0 PERCENT S 4 0 - 6 0 PERCENT K IOPERCENT

DURA P 45 PERCENT S 45 PERCENT K 10 PERCENT

D E L l DURA p 50-70PERCENT S 2 0 - 4 0 PERCENT K IOPERCENT

p S K

70-85PERCENT 5-20PERCENT 10 PERCENT

pISlFER~ P 99 PERCENT S OPERCENT K 1 PERCENT

Fig. 3.

Diagrammatic sections of the fruitlets of the oil palm showing variations in the proportions of components. (Drawing courtesy of Dr K. Tan.)

from the bruised fruit to the bunch waste. At present this oil (a third of the lost oil) is left adhering to the bunch residues. The oil-contaminated, more or less empty of fruit, wet bunches are conveyed to the incinerator (Fig. 4). Incineration is itself a cause of aerial pollution, apart from being a waste of low-grade heat. Incineration, however, produces a valuable high-potassic ash which is recycled to the plantations. The separated fruits are conveyed to a so-called digester, where they are held just below boiling point whilst being subjected to stirring in a baffled tank for about 10-20min. Some water may be added to the fruit; conditions of stirring, temperature and detention time are critical. F r o m the digester the fruit mash is transferred to a continuous screwpress in

Byproduct recot,ery in palm oil mills

Fig. 4.

37

Incinerator of palm oil mill used for disposal of bunch waste to produce a potassic ash.

which the pulp is squeezed out, leaving the nuts, together with the coarser pericarp fibre (also with adherent oil). Nuts and fibre are subsequently separated for cracking and burning, respectively. The nuts go for further processing to recover the kernels, and the shell is used as a boiler feedstock, road metal, or for the production of an activated carbon. Pyrolytic destruction is a potential processing method. Because of its high calorific value, the oily fibre is, together with the nut shells, the main feed for the furnaces. The palm oil mill is self-sustaining in energy and from the larger mills there is even a surplus. It is then available for use as an animal feed or as a source of cellulosic pulp. Treatment to recover the cellulose would also yield additional oil in the form of either solvent-extracted oil or soap stock. Since caustic soda treatment of the feedstock is normal in the pulp industries this pretreatment would not involve an abnormal operation, although the advantage ofoil recovery from an oily fibre has to be offset against the cost of the extra amount of caustic soda required above that for a non-oily fibre.

38

w. R. Stanton

The pericarp pulp consists of short fibres, ligno-cellulose dust, cell wall residues, cell contents, free-, emulsified-, adherent-oil, clay, sand and various plant organelles. This is pumped to settling tanks in a clarification station where the press slurry is held at a temperature near boiling point (85-95°C). The free oil rises and is skimmed off. Further free oil is separated from the decanted aqueous layer by means of sludge centrifuges. The original free oil is also clarified by centrifuges. From the sludge centrifuges the liquor is discharged at a temperature of 85-95 °C to a sludge pit where further oil-free oil emerges and is skimmed off by hand or, more recently, by mechanical oil mops. The final sludge, which has normally acquired contaminants e n r o u t e , is the palm-oil-milleffluent (POME) (Hwang e t a l . , 1978). It has a Total Solids content of 5-7 ~o, of which a little over half is dissolved solids, the other half being a mixture of various forms of organic and inorganic Suspended Solids (Table 2). It is to this sludge pit effluent that effluent treatment has been applied, with the exception that some investigators have interposed vibrating screens into the sludge discharge system before the effluent flows into the sludge pit. This pretreatment has the effect of removing some of the coarser, though not necessarily the heavier, Suspended Solids from the effluent. Whilst this processing may help some downstream treatments it cools the effluent and aerates it, both of which features may be disadvantageous. Loss of oil In practice this effluent ( P O M E), which is discharged at the rate of 0.6-0-7 tonnes per tonne of fresh-fruit-bunch harvested, contains a minimum of TABLE 2 Carbohydrate Constituents of Palm Oil Mill Effluent (Percentage on dry basis) (1) Total Sugars Starch Pectin (as Ca pectate) Pentosans

2.50 4.38 -

(2)

(3)

T r a c e Trace 7.30 9.23 1.45 3.20 10.80 4.51

(I) After Muthurajah (1976) (cited from Hwang et (1978)). (2) Sludge. (3) Condensate (after Hwang et (1978)).

al. al.

Byproduct recovery in palm oil mills

39

0.7 % ofoil as analysed by normal AOAC methods, and, frequently in the author's experience, it contains over 1% of oil. The quality of this aqueous phase oil is, at the settling tank, the same as, or even better than, that of the free oil. It only deteriorates subsequently as it cools, is aerated and mixed with contaminants in the course of passage to the sludge pit and to the effluent treatment system. Before any pollution control regulations were introduced the sludge was at this stage discharged into the estate. It gradually cools to ambient temperature and becomes diluted with water streams arising from other sources. At this stage further oil separates from the effluent stream (Fig. 5) and it has been the practice in the past for this to be gathered by gleaners. After reboiling it is sold as sludge oil. Although this sludge oil may have an FFA value ranging from 10 % to 50%, nevertheless it has industrial uses (for example, Free Fatty Acids and soap stock) and frequently fetches a price two-thirds of the price of crude oil on the open market. However, when cool and trapped, it contributes to the components of a scum blanket caused by the natural fermentation of the effluent in the stream. Gases from the fermentation float particulate matter to the surface and create foam (Fig. 5) on which microbial growth occurs, and this matted sludge blanket then completely excludes light from penetrating to the stream. Hence, the blanket inhibits any pollution abatement effects due to photosynthetic oxidation. The fresh fruit bunches themselves are expected to yield about 20 ~, of oil with good processing, so that the loss of bound oil to the aqueous phase constitutes a loss of 5 % of the nett revenue to the factory. The effluent itself has a Chemical Oxygen Demand of 50 000-70 000 mg litre- ' and a Biological Oxygen Demand of 20 000-35 000 mg litre- 1, the removal of which is now an obligatory charge on the cost of processing. Thus, pollutants have a debit accounting value, the population equivalent of a mill being that of a small town. Physical methods of byproduct recovery from the sludge and simultaneous pollution abatement In its simplest form the approach to the problem of pollution abatement with product recovery has been to dry the whole sludge to produce an animal feed. This concept is not new. It is widely employed in the fermentation industry for the disposal of distillation slops (Lewicki, 1979; Jackman, 1977), but the relative ash contents of palm oil solids and

40

W. R. Stanton

Fig. 5. Formation of scum blanket as effluent stream cools. Note free oil (black patch in middle distance) below the scum blanket. Thermophilic fungi coat the walls of the channel.

vinasse are not comparable. Whereas vinasse may be 20'Yo ash on dry matter (DM), with a relatively small component of acid-insoluble solids (dirt), ash from palm oil effluent may be 30 ~o ofthe total DM with 20 ~o of the ash being acid insoluble. The high ash content restricts use of dried effluent in compound feeds. Another method of disposal has been to distribute the raw effluent on the land. This is feasible where there is no danger of the material adventitiously entering streams, or forming an impervious blanket on the soil. Whilst land disposal is a relatively cheap solution and recovers all the nutrients, the crude sludge, being equivalent to an oily, muddy jam (Stanton, 1974), is liable to clog pipes and nozzles. The micro-aerophilic conditions and ambient temperature in the pipes are ideal for the growth

Byproduct recovery in palm oil mills

41

TABLE 3 Melting Points of the Triglycerides (~ polymorph) of the Principal Fatty Acids of Palm Oil

Constitution

Approx. %

Melting point (°C)

PPP POP PPO POO PLP

7 24 8 20 8

66-4 37.5 34.5 16.0 28-5

P = palmitate. O = oleate. L = linolenate. Unpublished data by courtesy of Dr K. Berger, PORIM, Kuala Lumpur.

of polysaccharide-forming coccoid bacteria, the bane of the sugar industry, thus adding to the danger of'clogging. In wet weather the sticky blanket makes the area where sludge is being spread impassable. The residual oil impedes evaporation. Were oil palms coconuts or doum palms, adapted to light sandy lands, then this land spreading would be the perfect solution; unfortunately, they are not, yielding their best on lowlying clays and other heavier water-retaining soils, hence the Malay name Kelapa Sawit, or swamp palm. Many of the components of the sludge, derived from the fruit, are emulsifying (proteins, polysaccharides) and thickening (pectins, gelatinised starch) agents, and it is these which inhibit the use, without pretreatment, of the commonly employed methods for filtration separation of components. Foodsafe flocculants have been tried. They are expensive and reduce the value of the material as animal feed. Further, flocculation and flotation or floc settling are the antithesis of separation; all the Suspended Solids are aggregated. If the sand, clay and lignocellulose particles are removed, the effluent is an excellent fermentation feedstock, having a 'fermentable solids' of between 0-5 and 4~o, depending on the organism used for fermentability assay. This property has been recognised by a number ofworkers and a large, pilot-scale, tower fermenter (20m 3) was employed by one company to culture fungal biomass (Aspergillus spp.) for animal feed. More selective organisms, such as the yeasts, would require an enzymic, dual organism (SYMBA/ PEI K I LO) or koji pretreatment of the feedstock before they could use the substrate effectively.

42

W . R . Stanton

Having generated an animal feed biomass, there then arises the problem of disposing of it. Oil palm estates may not have an adjacent animal industry. Because of the dangers which have arisen due to mycotoxins in the past, the world market has been reluctant to accept fungal animal feeds, although protein contents have been shown to be high (35-40 ~o) (Worgan, 1976). Another restriction on the marketability of the products has been the high ash content of unseparated material. By contrast in marketability, oil recovered during the effluent treatment is automatically part of the mill's market economy, the other saleable products being water and energy, although the value of the last two is dependent on locality. Liquor recycling and methane-assisted drying are already in commercial operation. Biotechnical methods for aqueous phase oil recovery

As part of the palm oil industry economy, the sludge oil has a ready market. The problem is, therefore, a technical one of economically inducing separation of that oil from the aqueous emulsion which the physical heating and centrifugal processes have failed to recover. Solvent extraction is widely used in the vegetable oil industry and has been considered as a technique for removal of oil from POME sludge. Such a process has been developed for direct application to the wet sludge (Sutanto & Kirkaldy, 1978). The process is quantitively efficient, but it is high in capital and recurrent cost. It leaves the non-oil components largely unchanged. However, in considering solvent extraction the distinction should be drawn between the esters of glycerol and the other lipids. These other lipids, phospholipids and other unsaponifiable and polar lipids, tend to migrate to the sludge and, whilst they may not be important in the bulk of the oil, they affect the lipid level of the solventextracted residue and, on analysis, appear as residual 'oil'. In solvent extraction of residues these hydrophobic compounds (including highly coloured carotenes and phenolics) are transferred to the solvent phase from whence they may need subsequent separation, thus adding to the cost of refining this oil (Olie & Tjeng, 1974). With solvent extraction of some of the other oilcakes this does not happen to the same extent (Tjeng & Olie, 1975). True maceration, the alternative to solvent release, as now widely employed in the fruit-juice industry, is not directly applicable to the palm

Byproduct recovery in palm oil mills

43

fruit to help release oil, since fermentation aided maceration would normally generate microbial lipases. These enzymes would, in turn, degrade the oil, whilst the other lyases were degrading other components. Some system had therefore to be found in which maceration took place without the danger of lipase activity occurring. Maceration would, in addition to cell disruption and separation, help overcome the problem of formation of emulsions, since the enzyme mixture generated would be exposed to degrade the protein, the hemicelluloses (Malmos, 1978; Pintauro, 1980) and pectins. It is these compounds which are responsible for stabilising the emulsion in the sludge. The system of coalescence, or its antithesis, stabilisation, of the vegetable fat globule from emulsions has features akin to that of manipulation of the milk fat globule; liberation and coalescence are required with ghee (clarified butter fat) production, globule concentration and size stabilisation are required for thick-cream formation, emulsion stabilisation in yoghurts (whether true or synthetic fermented milks) and homogenised milks. However, even the behaviour of emulsions in milk is not fully understood (Mulder & Walstra, 1974), although casein is recognised as the dominant stabilising agent (Olie & Tjeng, New Scientist, 1979; J. H. Prentice, personal communication, 1980). Applying maceration theory to palm oil separation, treating the separated fruit to flash pasteurisation and then applying specific macerating enzymes would be theoretically advantageous. Unfortunately, it appears that the present method of sterilisation, although cumbersome from the point of view of heat transfer, is essential to the release of the fruit from the bunch and shrinkage of the kernel from the shell. One might go back toa prior process in the oil-extraction sequence, pasteurise the whole fruit, and then apply enzymes to release the fruit from the bunch, before proceeding to the next step of applying enzymes to the fruit digestion, leaving kernel shrinkage to a later process as part of kernel-oil extraction. At present there are technical and economic constraints against application of this technique, so that it does not appear to be possible. True enzymic digestion of the separated fruit is technically feasible, although it would be aided by crushing (Beech, 1979) as with grapes. It would require a profound alteration in the present sequence of unit processes, including changes in residence time, temperatures and pH profiles, as well as changes in machinery. It would also add to the cost of processing due to the cost of enzymes, although this cost would be small if enzymic processing were to be adopted by the whole industry.

44

W . R . Stanton

Mashing processes As stated earlier in this paper, the constraints on maceration are that, because the maceration is required to aid food-grade oil recovery, not juice recovery or technical oil recovery, aerobiosis of the liquor is not acceptable as aeration lowers the quality of the oil; this constraint immediately excludes encouragement of organisms requiring oxygen for growth. The digestion should not generate any compounds which might affect bleachability or odour. Further, lipase activity should be arrested. Fortunately, lipases are temperature sensitive enzymes and are rapidly inactivated at temperatures of about 50°C. Further, most lipases are normally active only at neutral or alkaline pH values, so that acid conditions also inactivate them. Other constraints are that the oil should be maintained liquid and emulsion formation discouraged. Palm oil is more difficult to release fron solids than some of the other vegetable oils in that the higher melting point fractions do not melt much below 50 °C (Table 2); any process involving a requirement for the maintenance of the oil in liquid form would have to operate above this temperature. Indeed, for the final extraction much higher temperatures would be preferable, since the increase in temperature gives a concomitant reduction in viscosity, thus aiding centrifugal separation. Acidity helps in the destruction of emulsions and mineral acid is employed for analytical purposes in the estimation of oil in natural emulsions such as milk, by the standard Gerber or Bishop methods used by the dairy industry, for example. Temperatures above 50°C are no barrier to the growth of thermophilic bacteria and are advantageous to other aspects of process optimisation such as reaction rate. Exclusion of unwanted organisms at these temperatures is an added advantage, as well as the facilitation of gas removal.

Lactobaciilic fermentations An anaerobic, thermophilic, acidophilic (ATA) fermentation is currently employed for the production of lactic acid by Lactobacillus delbrueckii. To provide an inoculum, lactobacillic cultures can be induced de novo in silage-like fermentation set up at 50 °C or more, using the classical slicedcabbage technique. Thermophilic lactobacilli are employed in the fermentation of milks (Sandine et al., 1972) and are an endemic nuisance in the sugar industry (Carr et al., 1975). Thus an oil-quality protecting method of microbial maceration (Malmos, 1978) of the fruit pulp may, a

Byproduct recouery in palm oil mills

45

priori, be achieved by operating under anaerobic acidophilic conditions at 50 °C or over, under which conditions lipases are inhibited (NOVO, unpublished). These conditions are not inhibitory to many proteolytic, amylolytic and pectinolytic enzymes and these could be induced advantageously to operate at higher temperature. As with all developments in fermentation-process technology, there are many steps between study of the process in the laboratory and design of a full-scale continuous fermentation. Due to the large volumes of effluent involved (40 m 3 h - ~ in the largest mills) it was apparent that a highly optimised process, with short retention time, was desirable to avoid th.e use of very large tanks, if the process was to be commercially economical, fermentation processes having been described by Atkinson et al. (1980) as 'a lot of water with a dash of catalyst in large expensive containers'.

The Centriplus process The Centriplus process is a commercial development (Alfa-Laval, 1978) of the thermophilic anaerobic maceration concept discussed in the previous section. The flow diagram for a full-scale plant is illustrated in Fig. 6. The process has been operated on a factory scale, based on the effluent derived from the sludge pit, but, as has been mentioned, this effluent is variable in quality and quantity. For the future it is destined to be incorporated as an in-mill process, taking feedstock from the clarification station, whereby greater process control can be achieved and the present sludge centrifuges omitted. The main variations on the basic process depend on whether the fermentation and product recovery process is to be an addition to an existing mill or incorporated in the design of a new mill. The latter gains the capital-cost advantage of a fully integrated design. Variation in design also depends on the opportunity for use of the byproduct as dry animal feed, a direct-feeding wet sludg e, or solid fertiliser, as an alternative to a pipeline distribution system of liquid fertiliser. Solid, rather than liquid, distribution has the advantages of: maintaining accessibility to the palms at all times, obviating capital, recurrent and labour (if lines not permanent) cost of pipelines, avoiding of the danger of liquor entering waterways, and facilitating aerobic microbial breakdown of the sludge, since solids can be tipped into windrows. If bunch residues are also spread, distribution of solids will aid breakdown of these, if the latter are used as a base for the windrow.

46

W. R. Stanton

Yet other methods for the use of the liquor, freed from Suspended Solids, occur. These are: as a stock-feed liquor, particularly at weaning, to exploit scouring-control properties of lactobacillic preparations, as a recycled liquor to the oil-extraction process (this is not only of value where a mill is short of process water, but may be advantageous in aiding extraction and protecting the oil from oxidation), as a feedstock for high rate, thermophilic, methane fermentation, liquid metabolite (such as

tf ~

FLOWM(Tf.R

BALANCING TANK

TS~M~f~LTUI~

rLILC~LaUnf~ EN~YIdE TANK

Fig. 6.

Flow diagram of the Centriplus process.

47

Byproduct recovery in palm oil mills

alcohol), or biomass-producing fermentations, as a boiler feed water, after such treatment above and appropriate tertiary treatments, as a nonclogging irrigation liquor, as a non-silt-carrying liquor (for small mills) for direct discharge for treatment in anaerobic/aerobic lagoons, and as a feedstock for algal culture, particularly Chlorella of which thermophilic, acidophilic, mixotrophic strains (giving high yields of biomass per unit of pond area at low pH values and 40°C) have been found in Malaya.

~_~

TO a ~ c m c O,OL~CA

I

~SSC~ .6.L

oi.

~

c,,icJ ~

7-

~.~

I

[ OP ~ ,

CIP t I L T E R TANK

Fig. 6.--contd.

--~

48

W.R. Stanton

Performance

The accompanying performance charts have been derived from data generated operating an experimental plant during 1980 with an approximate throughput capacity of 12-5 m 3 of effluent, which is equivalent to the effluent from an 18 tonne h- i capacity of fresh fruit bunch to the mill. However, since the treatment plant can be run practically continuously, using a cleaning-in-place unit for the nozzle separator, whereas mills do not operate 24 h a day and are shut completely one day a week except for standby current and steam, this capacity is sufficient for a 30 tonne mill. The plant was run for a week continuously to test this point, but for operational reasons of the mill itself it was not possible to run on a 24 h basis for longer periods. This test proved that such continuous running would, however, be feasible. During the test runs, which, allowing for stoppages in the mill, were approximately half the expected time, the equipment recovered 100 m 3 of food-grade oil. This oil would otherwise have been lost, or recovered solely as methane, since the effluent was received after it had passed the sludge pit where delayed release oil is recovered. Thus, in a full year's operation, a reasonable recovery would be 300m 3 of oil equivalent in value to 40 5/0of the capital cost of such a plant. The main consumption of energy is in the separator and decanter electric motors (approximately 50 kW), but since the former can replace the standard sludge-separator in a new mill, the main energy and cost addition is that of a decanter. At present these machines are infrequently encountered in the natural product industries of developing countries, but it is likely that their use will be extended where power is available and high value byproducts can cover their cost. Personnel required is limited to one full-time labourer and 1/ 10th time each of a #itter and plant supervisor. Additional labour is required for sludge removal and spreading. This is in the form of a tractor and trailer. Alternatively, the wet solids may be pumped to a storage silo and trough-fed to livestock, an operation which may be highly automated. At the experimental plant the local herd of cattle acquired a taste for the sludge and congregated around the trailer, to the discomfiture of the herdsman, to whom the new 'feed' was not familiar. Performance charts

Figure 7 plots the daily content of oil in the effluent before and after treatment, but without decanting of solid. This second step removed a

Byproduct recovery in palm oil mills

49

'°I %

l

I$

'°I o,L

. \.~

o~L..., l

-.

,

_ i-

A ! " '--.

/'4'v

.

......

. . . . . . . . . . . . .

_~_J_

,

/'",

, . _.. .

-

.

.,--',,\ , . ~ ,

.

. . . .

.

, _

.

,

,

,

,

'AFt.

MAR.

................

~..

"-'I

/

.......

i

. . . . . . . . . . . . .

APR cont

J

i

MAY

. . . .

J

JLY

"l ' o~,

4v I

,

,

,

,

,.

AUG.

,

,

L

I

.

.

.

.

.

.

.

.

I

SEPT

Fig. 7. Daily oil content of final effluent discharge (lower line), in relation to oil content of influent (upper line), both expressed as percentage of oil in liquor. Dashed upper line indicates prolonged stoppage.

further 50 % of its residual 'oil' (hexane extraction assayed). So that the final liquor phase retains, under good working conditions, about 0.35 of oil whereas the incoming effluent, for example in May, contained as much as 2 ~ ofoil (Fig. 7). It will be noted that with regular operation the performance improved, although after each stoppage the process required 4-6 days to settle down. In contrast to the methane fermentation the ATA fermentation is self correcting and, as will be seen from the flow

W. R. Stanton

50

E "6 O z

,

o~

io

__1 is

~o

°Io oil

Fig. 8. Analysesofoil content in terms of histogram of frequencyof differentclasses of 'level of oil' (0' 1~o units, total of 150 analyses) in influent (Blank) and effluent(Shaded). chart (Fig. 6), provision is made for a seed tank to assist start-up in a production-scale plant. Some of the thermophiles are found to be obligate and this phenomenon accounts for the lag in recovery. At this stage in the development, application of sophisticated mono- or poly-cultures was not appropriate. The balancing effect of processing is shown in the histogram, Fig. 8. This Figure depicts the difference in the distribution ofoil contents before and after processing, using the daily oil levels of incoming (open histogram) and outgoing (cross-hatched histogram) effluent as variates. It will be seen that, in spite of wide fluctuation in the level of the oil in the incoming effluent, that emerging from the plant has a narrow range potentially normally distributed variation. In a full-scale plant a larger balancing tank would permit complete eradication of the weekend effect. The existing tank only held a reserve sutficient for 10 h overrun. Similar effects are observable for the removal and reduction in

Byproduct recovery in palm oil mills

51

./o q

55

-

-I ! 25~ I

l_J

| _ ~ I a . . . l l l . . l

MAR

45

APR.

I

"

/ /

1/

25

NN.

/

I /

.

s*

",, / ~5L_~

t

L _~_.l

%[.

~___a_

i

i

1-._~

,

..~.

,

,

MAY

,

,

I

,

,

,

JLY

,

L

_.s.

AUG

"l,

3s F -

I

. . . .

I',.

-- \ i ',.

_.

"

~ /

V

.-"~

,"

15'

\

: ",

,'^'-.

I

"~, ,'

. . . . . •

'AUG. cont

I

i

'

~.

.....

;

I

.

.

.

.

.

SEPT

.

.

.

.

J

Fig. 9. Daily level of total solids ( % TS) in influent (solid upper line) and ettluent (dashed lower line) through the plant. Dashed upper line indicates prolonged stoppage.

variation in the graph of the Total Solids of the effluent, Fig. 9. The interposition of the sludge pit between the mill and the plant meant that the level of Total Solids fluctuated widely, bearing in mind that approximately 50 ~ of the total is 'dissolved solids'. Thus, in mid-April and mid-August the performance lines converge due, probably, to trapping effects and this is reflected in the COD values, Fig. 10. This

52

W . R . Stanton

iO~Or-s~

0

I

L

A

J

I

I

I

I

I

I

L -~ .....

~-

i

I

I

I

I

MAR.

APR

100

75

""" ";" .

0

.

.

.

.

.

.

.

.

.

.

.

.

.

.

i

.

[

.

HAY

.

.

.

.

.

.

JLY

100

"/5

15

0

~ ]

t

i

i

~__

~-

l

l

l

AUG.

Fig. 10.

1

.

l

l

i

. ~ _ _ ~ _ ~ . . .

x..a___l

l

J

1

_l

SEPT

Daily COD of influent (Solid line) and effluent (Dotted line) through the plant. Dashed lines indicate stoppages.

performance is summarised in the Fig. 11 histograms. This Figure shows a drop of some 40 ~o in the COD of the final effluent, cross hatched histograms, from that of the incoming effluent, open histogram. In contrast to sampling the oil, however, it was only possible to take 'solids removal' readings after the decanter and, as previously stated, for reasons of limitation on running time imposed by the mill's operation (not only due to stoppages, but also to absence of regular facilities to remove the

Byproduct recot'ery in palm oil mills

53

e'~

N

u4."

c~ ©

v

o

F

._=

E

E 0 ¢-, ¢.,

SSelO qoee u! senleA Jo eoueJJnooo ~o,~oUerlbgJ-j

54

W. R. Stanton

separated solids), this sampling was sporadic. Nevertheless, the results are sufficient to demonstrate the potential of the process from the point of view of reducing the load of pollutants finally discharged, even omitting recycling of liquor, in that the 40 ~ of COD is removed in a retention time of 6 to 10 h, the higher figure includes balancing tank residence time, in comparison with the 20-30 day times currently quoted for ambient methanogenesis. Further, the fractions removed by the process, oil and larger particulate solids, are the material responsible for the long retention time for BOD reduction in the normal methanogenesis process. Added to this are the beneficial effects on reduced scum formation, due to oil removal, and the reduced need for desludging of the methane system, for which mills are currently incurring extra capital cost by installing pondtraversing desludging derricks, extra agitation in the tanks, or expensive conical-bottomed tanks. With the decanter in operation a rough measure of microbial biomass production may be made by using the total Kjeldahl nitrogen data routinely analysed for the effluents. Total Kjeldahl nitrogen values (TKN) range from 400-1100 ppm in the effluent with most values lying between 600 and 800 ppm. Whereas the fermentation has little effect on the 40

¢1 30

I

'5

I

O) 20

o #_ I

I I

<~ 5o

I

I

I

so 150

151 250

zst 350

....

I

~i ~,50

I ..........

451 550

~_.__

,~i

I

~ 550

Range, ppm

Fig. 12. Frequency histogram showing range in the daily mean reduction of Kjeldahl nitrogen (in parts per million) achieved by passage through the plant. This nitrogen is retrieved in the solids. Total of 150 values.

Byproduct recovery in palm oil mills

55

level of potassium and other dissolved salts, it has a marked effect on the TKN, as is illustrated in the histogram, Fig. 12. The histogram illustrates the frequency with which differences of a specific size occur in the value of the incoming and outgoing liquid effluent, the outgoing effluent being lower than the influent by approximately 25 ~ . This nitrogen is fixed and transferred to the decanted phase and enhances the feed value of the decanted solids in comparison with that derived from unfermented decanted material. Phosphorus might be expected to show a similar trend, but was not continuously analysed during the test period. Since the fermentation lowers the viscosity and assists sand removal at an early stage in processing, these combined effects, of lowering insoluble ash content yet increasing nutrient value, enhance the value of the Centriplus solids in comparison with that of their unfermented counterpart. The process as described herein was evolved within the constraint of feasibility in the context of current mill process sequences. Extrapolation of fermentation processes from the laboratory bench to the industrial scale involves many social and economic considerations, apart from the engineering transformation. The conclusions of the trials are: (a)

Scale up of these ATA fermentations is technically advantageous, under local conditions. (b) It permits the application of continuous effluent processing. (c) It makes economical mechanically aided continuous separation and filtration processes. (d) It assists retention of thermal stability in the system, since the temperature difference between ambient 27 + 5°C and thermophilic status is small. In practice the drop in temperature from 55 °C of squat 50 m 3 tanks over a 24-h period is less than 10 °C and could be reduced further with lagging and/or wind and rain protection. In fact, the converse problem occurs with the current generation of methane tanks for POME, in which 35 °C operation is attempted, in that the hot effluent requires cooling to this low temperature before injection into the tanks, as their volume is as much as 3000 m 3. The only unavoidable limitation to regular operation is the variation in fruit production at different times of the year. This seasonal variation differs from locality to locality, but may be as low as 50 ~ of full rate during trough periods. Otherwise, with the modem large mills (60 tonnes an hour), operating more than one process line and steam/energy generating

56

W. R. Stanton

system, the effluent processing unit may be similarly twinned, thus permitting continuous operation at 50 ~o capacity at all times and 90 ~o capacity at most times. With careful planning and machinery checks, maintenance requiring a process line shut-down can be made coincident with the fruit production trough. This ability to exploit all-year-round operation is almost unique in plantation agriculture. It explains why the oil palm, and potentially other palms (e.g. sago), are such economical crops and this process design advantage is the envy of the sugar industry, for example.

DISCUSSION As Davies (1978) has pointed out, there is no single solution to the problem of pollution arising from the palm oil industry. It has even been suggested that the non-oil component might in future be separated to provide feedstock for an organic chemical industry. However, in general, the amount of feedstock produced by an individual mill is an order of magnitude too small to make this concept attractive, except where simple processing can be applied and the partially finished product then collected from a number of mills for further processing, for a paper industry, for example. By variation of the Centriplus fermentation, higher titres of lactic acid might be achieved through the use of additives, Suspended Solids from bunch ash, for example, to maintain the pH at optimal level for growth of the preferred acidogenic organism. The product would then be concentrated by recycling prior to extraction, or the effluent preconcentrated by partial evaporation prior to fermentation. Whether lactic acid recovered from this process would be competitive with other feedstocks, with less mineral contamination, is debatable. An alternative product, after preconcentration, would be ethanol, but this process would also require alteration of the carbohydrates in the substrate, if conventional organisms are used. Other organisms than Saccharomycesspp. and other biochemical pathways are now under consideration for industrial ethanol production, but the economics of scale may preclude application of these fermentations to the feedstock under discussion. It is clear, however, that, once de-oiled and the Suspended Solids removed, the feedstock is versatile. Fermentation technology of the type described herein could also be applied to assist in the cleaning and separation of other components,

Byproduct recovery in palm oil mills

57

derived from palm oil processing, particularly the cellulosic components by a retting process. The carbohydrates, waste fats and Free Fatty Acids are all potentials for microbial biomass production, if cost competitive as feedstocks. However, for the economical production of these, separation of the fermentable solids from the inorganic and particulate solids, prior to the biomass fermentation, is desirable. At the same time, to aid the product recovery, the concentration of fermentable solids should be raised to a high level, 10 % or more, although there are alternative views on this from proponents of tower fermentors and self-flocculating (self concentrating) organisms. An alternative use for the whole light-solids biomass, derived from the Centriplus fermentation, is for direct wet feeding at about 20% dry matter, as against drying and compounding into other animal feed. If a livestock industry is located close to a factory then there is no point in going to the additional expense of drying the wet material, since, from the author's experience, it conserves itself well for several weeks at ambient temperature, by ensilage, if maintained in an anaerobic state. Further, it is highly attractive to cattle and pigs and the act of drying tends to detract from some of the beneficial properties of the original wet material. From observation the acid liquor tends to remain in a stable condition for 3 or more weeks if kept in a sealed container, especially if packed at the temperature of discharge (i.e. pasteurised). It may thus be conserved to regulate the supply of feedstock to high-rate methane generators, such as those described by van Beilegem (1980). Centrifuges are normally considered as methods for [liquid/liquid separation, or liquid/solid separation, although they are capable of extracting more than one solid phase, either sequentially or simultaneously. That is, they are the antithesis of the previously mentioned flocculation process, which aggregates components of the suspended solid together, irrespective of their specific gravity. This contrast in action of the centrifuge to gravity flocculation settling is partially due to the fact that the act of centrifugation may destroy through shearing, depending on the design employed, low density flocs. This property is employed advantageously in the Centriplus process, in which the sand, silt and clay fractions are rejected prior to applying the cleaned liquor to further processing. Similarly, the centrifuge, which is normally regarded as a post-fermentation piece of equipment, may be employed as an alternative to floc/gravity settling, for maintenance of the level of active biomass in a

58

W . R . Stanton

fully mixed fermentation reaction by recycling a selected light solids fraction of the solids. The same principle can be employed to decontaminate, separate bacteria from yeasts, separate the purple bacteria from algal cultures, or even size grade eukaryotic cultures (e.g. yeasts, algae). The steady state, assessed by on-line measurements, of the continuous self-optimised Centriplus process is achieved by manipulation of the residence time and the rate of recycle, using a decanter to control the level of solids in the reactor. Operating at the high temperature controls the population of organisms in favour of the preferred species. This is further aided by careful control of the degree of aerobiosis. Operating at a high temperature assists in maintaining anaerobic conditions through the reduced solubility of oxygen at higher temperatures. Rate of growth of particular microbial components could be increased further by controlled neutralisation of acidity, but this would counteract the good effect of the acidity on the breaking of the emulsions. Pectins, in particular, are stabilised by the addition of calcium ions to a solution (El Tinay et al., 1979). Prior removal of all long fibre and heavy abrasive material has permitted long periods of continuous running of the equipment with minimal breakdown and a low replacement rate for spare parts. The present design, operating at a temperature related to that of the effluent discharge temperature from the mill, makes minimum demands on cooling; the additional heating required is available from the low-grade exhaust steam from the steriliser. This demand for steam is minimal due to a high ambient temperature in Malaya and the large capacity of the vessels involved in the fermentation. It was the problem of cooling the effluent, encountered in early work on the design of treatment systems by the author, which prompted the study of operating of the whole process in the thermophilic range. Neither microbially aided digestion, nor enzyme aided digestion, for the release of vegetable oil is a new process. A lactobacillic fermentation has been applied to coconut processing (Puertollano et al., 1970), but it does not appear to have been taken up commercially because of long residence time required. Enzymic digestion has been shown to increase the yield of oil from olives and, due to the high value of this oil, this appears to be an economical process (Malmos, 1978). It is the combination of effects of the Centriplus process which makes it attractive and, because of its simplicity, it is applicable in various forms on a large or small scale. The principles of control of the thermophilic fermentation (temperature; control of degree of aerobiosis and level of

Byproduct recovery in palm oil mills

59

active biomass by centrifugal separation) have wide application and do not appear to have been well exploited by the fermentation industry. Reasons for this are partly attributable to the fact that the virtues of the ATA fermentation, as a process in its own right, have been obscured by being regarded as a stage in the thermophilic methane fermentation, but, where valuable intermediate products can be extracted from the fermentation, then the methane component should, in the author's opinion, be considered as the fermentation of last resort. An additional feature of this prefermentation is that it can be used to control the rate of methane supply, to meet variable gas demand, by a simple prefermentation and a non-pressurised reservoir to hold the product of the first stage. This compares with the complication required for conservation of the gas itself, either in gas holders, or compressed. The solid extracted silage may also be used as a conserved form of methane gas, but the rate of digestion is less rapid than that of the liquor and is not as easily applied to control of gas production as is the liquid portion of the silage. It is somewhat paradoxical that lactic acid generated in the ATA fermentation is not recovered. Yet this acid is added to some makes of margarine which use palm oil as a base. Lactic acid preparations are also used in therapeutic toilet soaps (Beech, Canada Weekly, 1981).

Microbiota In this discussion, the r61e of the key element, the microbiota, has been largely omitted. As is to be expected, a novel environment might contain a novel biota. This is borne out in practice, but until further characterisation of the isolates is carried out it is not possible to state how far those isolates at present obtained differ from textbook species. The frequency of occurrence of thermophilic sporeformers is higher than anticipated, but this may be in part an artefact of frequency of shut down o f the mill and hence the plant.

Economy The current emphasis on BOD, rather than COD, in the assessment of the pollution ofwater in the temperate zone needs qualifying under the highly bioactive conditions of the tropics. For the latter, the time taken for a compound to degrade and the assumed stability of specific organic molecules require reconsideration. Under tropical conditions the need to lower COD cannot be ignored. Thus, by reducing COD the Centriplus

60

W . R . Stanton

process effects economies in the effluent treatment for BOD reduction. No evidence of toxicity in the extracted solids has been detected, either when these have been fed wet ad lib. to pigs and cattle, or as a major component of dried compound feed to poultry. A further economy is achieved in the size of pollution treatment plant by the recycling process. Indeed, both the liquor and solids appear to have beneficial effects. The former on viscosity reduction and protection against oxidation in the oil extraction and the latter in improving the feed to gain ratio, when applied at up to 25 ~o of the feed, on poultry ration. No evidence of the postulated toxicity mentioned by Wong (1979), or the adverse effects of reduced sulphur compounds has occurred, although the predictions may be relevant to the solids derived from the methane fermentation. The goals of the two fermentations are apposite although, as mentioned elsewhere in this paper, both the post-Centriplus liquor and the solid may be applied to the methane fermentation. They provide a reserve of conserved feedstock and thus assist the latter process. However, it appears difficult to justify the transformation of complex carbohydrate and protein molecules, synthesised at energy and other costs--t, iz. the products of the harvest--to methane, if those molecules can be separated and their intrinsic value realised, even if this is only the liquid fuel value of the palm oil (Wong, 1981). Methane as an economic product of a protein, fat, carbohydrate mixture is a goal of last resort, suited to faecal or noxious material, and does not reap the full benefit of the palm fruit for food or feed (Stanton, 1974). Finally, under humid tropical conditions humus is at a premium (Jenny, 1980) and one company in Malaysia, which has adopted a method of separating and drying the sludge solids for fertiliser, has shown the dramatic benefits of applying this philosophy. As in the Centriplus process, the liquor is recycled so that, eventually, the soluble nutrients end up in the dried solids. Waste flue-gas heat is used for drying and for fertiliser; the high ash in the resultant solids is not deleterious as it is in animal feed. However, the wet solids from separation without prefermentation are less easily recovered because of the higher viscosity, contain more entrained oil and are liable to go rancid. CONCLUSIONS Fermentation processes for methanogenesis have already been accepted by the palm oil industry. Initially, the reactors were simple holes in the

Byproduct recot~ery in palm oil mills

61

ground, using the fermentations solely for BOD reduction. From this beginning the industry has progressed to stirred tank reactors up to 3000m 3 capacity with facility for gas collection, using the methane for dryers. It is likely that more sophisticated reactors will be acceptable within two years, if methane continues to be the preferred product of the sludge fermentation. An equivalent evolution in technique is taking place in oil recovery and component separation, the first stage being the gleaners of oil and the second the elaboration of natural-settlement oil-trapping devices. As with gleaning, in the operation of these oil traps there is no clear distinction in the process between the recovery of free oil and recovery of a further increment of oil from the emulsion by adventitious microbial reaction. Future high rate reactors for methane fermentation will be matched in the mill by biotechnical reactors separating and recovering components more completely and with a better process economy, in terms of machinery and energy, than at present. The bonus, the '-plus' in Centriplus, will be a range of high quality, largely additive free, food, feed and industrial materials, thus achieving the goal of utilising all the biomass harvested. Thus, what at the outset was a study on the biology of an effluent treatment system, has become an in-mill biotechnological concept indicating the virtue of radical modification of the vegetable oil extraction process itself, having, in consequence, widespread implications in relation to determining the appropriate process engineering for improved extraction of the oil and for enhancing, through fermentation and separation, the value of the other raw materials present in the fruit. REFERENCES Alfa-Laval (1978). Processing of effluent from palm fruit extraction. UK. Pat. app'n No. 34203/78 (Pub. Ser. No. 2007205) Alfa-Laval. Tumba. (Inventor, W. R. Stanton.) Atkinson, B., Black, G. M. & Pinches, A. (1980). Process intensification using cell support systems. Process Biochemistry. 15, 24-32. Beech, F. W. (I 979). Wine making with English fruit. The Garden, 104, 289-93. Canada Weekly (1981). Canadian yogurt company savours popularity abroad, Canada Weekly, 9, 5. Carr, J. G., Cutting, C. V. & Whiting, G. C. (Eds). (1975). Lactic acid bacteria in beverages and food. Academic. Press. London, New York, San Francisco. Collier, H. M. & Chick, W. H. (1977). Problems and potential in the treatment of rubber factory and palm oil mill effluents, Planter, Kuala Lumpur, 53, 43948.

62

W. R. Stanton

Davis, J. B. (1978). Palm oil mill effluent: A review of methods proposed for its treatment. Trop. Sci., 20, 233-62. El Tinay, A. H., Saeed, A. R. & Bedri, M. F. (1979). Fractionation and characterization of guava pectic substances. J. f d Technol., 14, 343-9. Hwang, T. K., Ong, S. M., Seow, C. C. & Tan, H. K. (1978), Chemical composition of palm oil mill effluent. Planter Kuala Lumpur, 54, 749-56. Jackman, E. A. (1977). Distillery effluent treatment in the Brazilian national alcohol programme. Chem. Eng. (April, p. 4). Jenny, H. (1980). Alcohol or humus? Science, 209, Aria (citing Aaltonen, V. T. (1948). Boden und Wald. Parey, Berlin) Supplement. Kirkaldy, J. L. R. & Sutanto, J. B. (1976). Possible utilization of byproducts, Planter, Kuala Lumpur, 52, 118-26. Lewicki, W. (1979). Production, application and marketing of concentratedmolasses-fermentation effluent, U NIDO workshop on fermentation alcohol, fuel and chemical feedstock. Paper ID/WG 293/22/Rev. I (mimeo), UNIDO, Vienna. Maheswaran, A. & Singam, G. (1977). Pollution control in the palm oil industry-promulgation of regulations. Planter, Kuala Lumpur, 53, 470-6. Malmos, H. (1978). Enzyme applications in food, pharmaceutical and other industries: Industrial applications of cellulases. A I ChE Symposium Series, Food, Pharmaceutical and Bioengineering, 1976/77, 93-9. Mulder, H. & Walstra, P. (1974). Isolation of milk fat. In: The milk fat globule, 228-45, Comm. Bureau Dairy Sci. Tech., Reading, Great Britain. Myers, N. (1978). Forests for people. New Scientist, 80, 951-3. (Specific reference to disappearance of tropical rainforest in Malaysia.) Olie, J. J. & Tjeng, T. D. (1970). Notes on the treatment anddisposal of palm oil mill effluent, Stork N.V., Amsterdam. (Mimeo), p. 21. Olie, J. J. & Tjeng, T. D. (1974). The extraction of palm oil. Stork-Amsterdam N.V., Amsterdam (Mimeo). (I 979). Technology-creamed off research helps pudding eaters. New Scientist, 84, 943. Pintauro, N. D. (1980). Byproduct and waste utilization and animal feed production. J. f d Technol., 52, 384-411. Prentice, J. H. (I 980). Letter to the author (13.8.80) from Dr. Prentice, Nat. Inst. Res. Dairying, Reading, UK. Puertollano, C. L., Banzon, J. and Steinkraus, K. H. (1970). Separation of the oil and protein fractions in coconut (Cocos nucifera) by fermentation, J. Agric. f d Chem., 18, 579-84. Sagan, C., Toon, O. B. & Pollock, J. B. (1979). Anthropogenic albedo changes and the Earth's climate. Science, 206, 1363-8. Sandine, W. E., Radich, P. C. & Elliker, P. R. (1972). Ecology of the lactic streptococci. J. Milk Fd Technol., 35, 176-84. (A review, 72 refs.) Singh, K. and Ng, S. H. (! 968). Treatment and disposal of palm oil mill effluent. Malaysian agric. J., 46, 316-23. Stanton, W. R. (1974). Treatment of effluent from palm oil factories, Planter, Kuala Lumpur, 50, 382-7.

Byproduct recovery in palm oil mills

63

Sutanto, J. B. (1979). Total utilization of byproducts from palm oil industry, Chemasia, Singapore. (Mimeo.) Sutanto, J. B. & Kirkaldy, J. R. (1978). Treatment of palm oil mill processing effluent by solvent extraction. UK Patent app'n 26675/78 Pub. as Ser. No. 2 023 120 28/12/79. Tjeng, T. D. & Olie, J. J. (1975). Why solvent extraction of palm oil is not to be recommended. Oleagineux, 30, 523-8. van Bellegem, Th. M. (1980). The elimination of organic wastes from surface water. In: Proceedings 13th International TNO Conference. "Biotechnology, A Hidden Past, A Shining Future.' TNO, The Hague. Wong, K. K. (1979). Ecological significance of biogas generation from palm oil mill effluent as a non conventional energy source in Malaysia. 6th Int. Syrup. trop. Ecol., Univ. Malaya, Kuala Lumpur 16-21/4/79. Wong, K. K. (1981). Soft energy from palm oil and its wastes. Agric. Wastes, 3, 191-200. Worgan, J. T. (1976). Wastes from crop plants as raw materials for conversion by fungi to food or livestock feed. In: Food from waste (Birch, G. G., Parker, K. J. & Worgan, J. T. (Eds)), Applied Science Publishers, London.