FIELD OF THE INVENTION:
This invention relates to an algal biomass dewatering system and an adsorption process used therefore.
BACKGROUND OF THE INVENTION:
Separation of algal biomass from the bulk suspension (cultivation froth) is an essential step for mass production of commercially viable products. Depending upon the microalgal properties, harvesting technique is selected, which includes two major steps. The first step comprises of bulk water removal that could be attained by using flocculation, flotation, gravity sedimentation, filtration and centrifugation methods. Next step involves concentration of the initial biomass slurry obtained thereafter by implementing sun drying, vacuum drying and heat treatment techniques. Bulk water removal step can only remove up to 2-7% of the total moisture, indicating requirement of methods/techniques involved in thickening of the moisture laden slurry, a major step in downstream processing. The processes or methods involved are either not much efficient or extremely energy intensive.
Microalgae, belonging to the lower phylogenetic echelons of the plant kingdom are basically miniature sunlight driven cell factories that convert carbon dioxide into biofuels, foods, feeds and value added products of commercial importance. In spite of having enormous advantages over conventional biofuel sources, commercialization of microalgae in terms of biofuel production is restrained due to high operational cost for downstream processing. High moisture content (98-99%) of the initial algal slurry obtained after harvesting makes it

imperative to add the dewatering step in downstream processing. In this respect, a huge chunk of money and energy is invested to dewater algal cells followed by bulk water removal. High cost inputs for production and downstream processing of algae makes it economically unattractive substrate for the commercial production of biofuel. Limitations encountered while harvesting the algal biomass is due to the size, specific gravity and morphology of the algal cells. This kind of economic and technical problems of algal dewatering has been a major obstacle for large scale biofuel production.
Biomass is subjected to various dewatering methods to shed off the extra water as stated in the earlier reports. Basically the methods followed include filtration, gravity sedimentation, flocculation, electro-flocculation, flotation, adsorptive bubble separation, bubble column, etc (Grima et al., 2003). Initially bulk water is removed from the slurry by applying one or combination of these techniques. Filtration process suffers primarily from unsatisfactory biomass recovery due to relatively low filtration rate. Microalgal cells carry negative charges, which inhibits their aggregation in suspension. Multivalent metal salts such as ferric chloride (FeCl3), aluminum sulfate [Al2 (SO4)3,], ferric sulfate [Fe2(SO4)3] etc are used as flocculants or coagulants for harvesting algal cells from initial slurry (Benemann et al., 1980, Moraine et al., 1980). Other than metal salts, polymeric flocculants have also been used profoundly for recovering algal biomass (Pushparaj et al., 1993). In case of bubble column or adsorptive bubble column mediated dewatering process algal cells get attached with the air bubbles sparged inside the column and rendered its separation from the bulk solution (Kanel et al., 1999).

Cumulative analysis of the prior reports indicates that the technologies employed for dewatering of algae are concerned with the bulk removal of water from the initial algal slurry. In true sense the actual removal of water from the algal cells (dehydration of biomass) are done by conventional methods such as heat drying, spray drying, freeze drying, sun drying and vacuum drying (Grima et al., 2003). The methods reported as prior art has several disadvantages due to their energy intensive and time consuming nature.
OBJECTS OF THE INVENTION;
It is therefore an object of this invention to propose an algal biomass dewatering system which is efficient.
It is a further object of this invention to propose an algal biomass dewatering system, which is cost-effective and simple.
Another object of this invention is to propose an algal biomass dewatering system which is eco-friendly.
Yet another object of this invention is to propose an algal biomass dewatering system which is easily operable and robust.
These and other objects and advantages of the invention will be apparent from the ensuing description, when read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig. 1: Algal biomass dewatering system
(a) Top view of the unit
(b) Front view of the unit

(c) Algal flakes obtained after 1h of exposure
Fig. 2: Plan view of the dewatering system according to the invention
(a) Front view of the system
(b) Top view of the system
Fig. 3: Flow diagram depicting the process according to the invention
DETAILED DESCRIPTION OF THE INVENTION;
Thus according to this invention is provided an algal biomass dewatering system and an adsorption process used therefor.
In accordance with this invention, an algal biomass dewatering (designated as ALGORBENT) (Fig. 1) has been developed, as also an efficient and cost-effective process for the removal of unbound and bound moisture from concentrated algal biomass slurry in an eco-friendly manner. The system can be used for dewatering microalgae and macroalgae. The microalgae that can be dewatered using the system according to the invention are filamentous algae such as Phormidium tentue, spirulina minima, microspora sp, oscillatoria sp., unicellular algae such as chlorella variabilis, chlorella vulgaris, chlorococcum infusionum. The macroalgae that can be dewatered are brown algae such as Cystoseria baccata (plant like thallus), Fucus sp. (thallus and frond), Laminaria sp. (claw like hold fast and laminated blade) and red algae such as Calliblepharis jubata (branched rhizoidal holdfast), Fucus sp. (mainly wrack, sometimes spiralled rack). The system (1) consists of four trays/cassettes (2) filled with reusable natural adsorbent and covered with lint free cloth (3) for rapid removal of algal water. The system involves the process of batch adsorption by an efficient and inexpensive

adsorbent used in top-open trays placed on a base plate (4) provided with at least two rollers (5), one located at a first end and another located at a second end of the base plate (4). The base plate is equipped with reflectors/mirrors (6) placed at suitable angles. Four rotatable reflectors (4) with flexible angle are placed along the trays so that they can be rotated according to the movement of the sun. Reflectors are used to focus the sunrays onto the trays so that the adsorbing material can be reused for a minimum of 15 batches with an average moisture removal efficiency of 75%. The trays are fitted with the ground adsorbent and a lint-free cloth (3) is stretched over the trays and over two rollers (5) at the two ends. The rollers can be rotated by means of a handle (7). The dried algal biomass can be scraped off from the lint free cloth by scraper (8) (Fig 2).
The process is further accelerated by preventing a state of equilibrium from setting in by carrying it out under the Sun and using reflecting mirrors as it was observed that the efficiency of the developed system was increased with rise in temperature. For this study, the equilibrium moisture contents of the adsorbing material and different algae were determined. Accordingly, the adsorbing material of different particle size was screened to determine the optimal adsorption pattern related to the size of the material used. Adsorption isotherm (Langmuir) was performed to determine the maximum adsorption capacity of the material. About 80-90% removal of water could be achieved in 1-1.5h, depending on the type of alga used. It could effectively remove water from the concentrated algal slurry up to 15 batches, preferably 9-10 batches. In first few batches, about 80-90% (w/w) removal of water could be achieved in 1-1.5h, depending on the type of alga used. On an average, it could

effectively remove 60-90% moisture from the concentrated algal slurry in 10 batches. After 10 batches of 1 hour duration each, from 20 kg of wet biomass, 2.66 kg of dry biomass (still containing 15% removable moisture) of Chlorella variabilis was obtained per kg of the adsorbent. The total surface area of the four top open trays/cassettes was 1600 cm2 with an average thickness of about 4 mm. After 10 batches, the adsorbent was regenerated by Sun drying for reuse.
The process according to the invention comprises the steps as shown in the flow diagram in Fig. 3 of the accompanying drawings. The adsorbing material used an inorganic material, mostly containing alumina (Al2O3), (SiO2), Ferroxide (Fe2O3), (Ti) titanium and (K2O) potassium oxide. This adsorbent material is ground into particles of suitable size, usually ranging from 1 mm to 5 mm. The material composition of the adsorbent is as follows:
Al2O3 : 44-46.5% by weight
SiO2 : 47-50% by weight
Fe2O3 : 0.75-3% by weight Ti: 0.5-2% by weight K2O : 0.25-2% by weight
Remaining 2% is made up of other minor components
The adsorbent material is ground to a suitable particle size, preferably 1 to 5 mm. The top open trays/cassettes are filled with the ground adsorbent and the device (ALGORBENT) is placed outside under the sun, so that it receives an average temperature of 20 to 250°C. Concentrated microalgal slurry is poured on the trays covered with lint free cloth. The lint-free cloth acts as an interface between the ground adsorbent and the

algal biomass, to prevent the biomass from coming in contact with the adsorbent. This eliminates any further steps of cleaning the biomass after drying. The lint-free cloth has an advantage over ordinary cotton fabrics as it prevents the dried biomass from adhering to it. The algal biomass placed on the lint free cloth, is dried over the adsorbing material for about 1 to 1.5 hrs, by which time, 80 to 90% of the moisture is removed. Once the moisture is removed, the lint free cloth is allowed to travel over the rollers by turning the handle, to effectively offload the dried biomass therefrom. Thereafter, a fresh batch of algal biomass is taken for drying in a similar fashion. The process has been outlined in the flow diagram shown in Fig. 3.
Implementation of this kind of dewatering system is expected to
drastically reduce the overall downstream processing cost and energy
input in algal research for biofuels and other applications. Thus this
novel algal biomass dewatering system is characterized by its simple
design, ease of operation, reusable inexpensive adsorbent, minimum
energy input and high efficiency in dewatering of concentrated algal
biomass. The dewatering system and the process used therefor that was
developed to achieve 80-90% removal of bound and unbound water from
the concentrated slurry of algal biomass consists of the following major
steps.
(i) Identification of the right adsorbent for dewatering of wet algal biomass
(ii) Screening of particle size of the adsorbent for effective adsorption
(iii) Studying adsorption isotherm to understand and establish the
mechanism of dewatering
(iv) Determination of equilibrium moisture contents of the adsorbent and
different algae
(v) Determination of duration/time to attain moisture content close to
bone dry state

(vi) Determination of the effect of temperature on dewatering of different
algae
(vii) Determination of recyclability/reusability of the adsorbent
(viii) Design and fabrication of the dewatering system based on above
inputs and information
The invention resides in the development of a novel easily operable, robust and inexpensive algal dewatering unit comprising of readily available, recyclable adsorbent in tray/cassette form with high water removal efficiency (80-90% of initial moisture content of algal biomass could be removed) and minimum energy input. The process is simple, cost-effective and uses readily available adsorbing material. It has a high dry biomass recovery rate as compared to conventional dewatering methods and high recyclability. Therefore there is almost no wastage of the absorbing material. The system is robust irrespective of algal morphology, independent of environment influences and allows minimum loss of biomass. It has tremendous potential in biofuel manufacturing as well as marketing companies; Healthcare and Nutraceutical companies; Algal companies; Process industries producing large volume of waste water; Mining industries for metal remediation; Common/rural people and farmers, Patients, Catties and Aquaculture animals/fishes.

WE CLAIM;
1. A system for de-watering of algal biomass in an accelerated adsorption
process, comprising:
-a base plate provided with at least two rollers one each located at a first
and second end of the base plate and provided with handle;
-a plurality of cassettes axially disposed along the base plate and
accommodating a ground adsorbent material;
-a plurality of rotatable mirrors disposed along the base plate at different
angle, operably covering said cassettes such that the mirrors can be
rotated corresponding to the positions of sun and focus sunrays onto the
cassettes; and
-a lint free cloth placed on the cassettes over the heated adsorbent and
slidably held over the rollers at the two ends
-concentrated microalgal slurry placed on the lint free cloth for a
predetermined period to allow removal of moisture from the slurry.
2. The system as claimed in claim 1, wherein the adsorbent is a naturally occurring inorganic material mainly comprised of alumina (Al2O3), silica (SiO2), ferric oxide (Fe2O3), Titanium (Ti) and potassium oxide (K2O).
3. The system as claimed in claim 1,2 wherein the adsorbent material has the following composition
Al2O3 : 44-46.5% by weight SiO2 : 47-50% by weight Fe2O3 : 0.75-3% by weight Ti: 0.5-2% by weight K2O : 0.25-2% by weight
4. The system as claimed in claim 1, wherein the adsorbent material is
ground to a particle size of 1 mm to 5 mm.

5. The system as claimed in claim 1, wherein cassettes have a total surface area of 1600 cm2.
6. The system as claimed in claim 1, wherein the cassettes have an average thickness of 3 to 5 mm.
7. The system as claimed in claim 1, wherein the algal biomass is dried for a period of 1 to 1.5 hours whereby 80-90% of the moisture is removed.
8. A process for dewatering of algal biomass comprising the steps of grinding raw adsorbent,
filling the trays of the system as claimed in claim 1 with the ground
adsorbent,
the system is placed outside in the sun,
concentrated microalgal slurry is poured on the lint free cloth covering
the trays and adjusting the reflectors to focus sunlight onto the algal
biomass,
allowing the algal biomass to dry over a period of 1 to 1.5 hours.
9. The process as claimed in claim 8, wherein the drying is conducted at
a temperature in the range of 20 to 25°C.
10. The process as claimed in claim 8, which is repeated for upto 15
batches with the same adsorbent.