ANAEROBIC PHOTOBIOREACTOR AND METHOD FOR BIOMASS CULTIVATION, WASTEWATER TREATMENT, NUTRIENTS RECOVERY, ENERGY PRODUCTION AND HIGH-VALUE PRODUCTS SYNTHESIS

Abstract

The present invention is related to an anaerobic photobioreactor and a method for active biomass cultivation, wastewater treatment, nutrients recovery, energy production and high-value products synthesis. Phototrophic bacteria are cultured in the anaerobic photobioreactor lighted with solar or artificial irradiation where certain light wavelengths are selectively discarded with a light selector installed on the top of the photobioreactor. In this light-based process wastewater treatment and resources recovery, like nutrients and high-value bioproducts (fertilizers, polymers and proteins) present in wastewater are performed simultaneously. Cultured biomass is treated by anaerobic digestion for biofuel production, including optative hydrolytic pre-treatment, and/or valuable bioproducts can be obtained in a downstream process.

Claims

1. An anaerobic photobioreactor for biomass cultivation, wastewater treatment, nutrients recovery, energy production and high-value products synthesis, comprising: a. a horizontal closed anaerobic ditch; b. an inlet and an outlet of wastewater, both connected to an internal space of the anaerobic ditch body; c. a covered wastewater circulation system inside the anaerobic ditch; d. a lid covering the anaerobic ditch to block light at wavelengths below 750 nm; e. a cylindrical sampling tube submerged into the anaerobic ditch and stuck to the lid, to perform water and biomass analysis and control the headspace pressure; f. a biomass recirculation pipe from a biomass to the anaerobic ditch; and g. a biomass outlet line from the biomass separator.

2. The anaerobic photobioreactor according to claim 1, wherein the photobiorector is lightened with a light source characterized by a wavelength between 750 and 1200 nm.

3. The anaerobic photobioreactor according to claim 2, wherein the light is solar irradiation.

4. The anaerobic photobioreactor according to claim 1, wherein the covering lids are made of glass or PPMA, and the selective monochromatic films are made by wavelength shifting compounds as aromatic cyano fluorophores, cyanine dyes as 1,1,2-Trimethylbenzindoleninium 1,3-disulfonate, 5-carboxy-1-(4-sulfobutyl)-2,3,3-trimethyl-3H-indolenine 2, and 1-(4-sulfonatobutyl)-2,3,3-trimethylindoleninium-5-sulfonate, or N-Ethyl-2,3,3-trimethylbenzindoleninium 5,7-Disulfonate.

5. The anaerobic photobioreactor according to claim 1, wherein a reactor headspace is connected to a gas exit, wherein biohydrogen produced by photofermentation is collected.

6. The anaerobic photobioreactor according to claim 1, wherein said headspace is connected to a N.sub.2 source to sparge the reactor.

7. The anaerobic photobioreactor according to claim 1, further comprising an anaerobic post-treatment in an anaerobic digester of the biomass cultivated, carried in the biomass outlet line.

8. The anaerobic photobioreactor according to claim 1, wherein said biomass outlet line is connected to a hydrolysis pre-treatment.

9. The anaerobic photobioreactor according to claim 1, wherein a sludge line exit from hydrolysis pre-treatment is connected to a downstream process to produce biopolymers, proteins or organic fertilizers.

10. Method for biomass cultivation, wastewater treatment, nutrients recovery, energy production and high-value products synthesis by using the anaerobic photobioreactor described in claim 1 comprising: (a) feeding the wastewater stream to the horizontal closed anaerobic ditch; (b) exposing the anaerobic phototrophic biomass to light under anaerobic conditions to assimilate organic matter and inorganic nutrients, while PPB biomass is cultivated; (c) circulating the wastewater through the anaerobic ditch by means of a covered circulation system; (d) separating the phototrophic biomass from the liquid phase by biomass separator where free-living bacteria are washed out from the system; (e) recirculating settleable biomass through a recirculation pipe to control the sludge retention time within the photobioreactor; and (f) treating the biomass cultured by anaerobic digestion to obtain biogas as energy source.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0056] The following Figures are described below. These illustrate the exemplary embodiments and are not limiting their scope.

[0057] FIG. 1 shows a top view of the photobioreactor and the cover lids.

[0058] FIG. 2 shows an anaerobic photobioreactor system according to an embodiment of the present invention

[0059] FIG. 3 shows an anaerobic photobioreactor system according to another embodiment of the present invention.

[0060] FIG. 4 shows the separation and purification of valuable bioproducts downstream (401), consisting on a extraction stage (402), followed by a separation process (403), where the residue of this process can be anaerobically digested (405), and a final stage of purification (404) to obtain high purity/quality products (406).

[0061] FIG. 5 shows PPB organics and nutrients assimilation experiments examples. Time-course of soluble COD (a), nitrogen (b) and phosphorus (c) in batch tests for wastewater type 1. Experiment id 1 (squares), 2 (circles) and 3 (triangles).

[0062] FIG. 6 shows PPB organics and nutrients assimilation experiments examples. Time-course of soluble COD (a), nitrogen (b) and phosphorus (c) in batch tests for wastewater type 2. Experiment id 4 (squares), 5 (circles) and 6 (triangles).

DESCRIPTION OF EMBODIMENTS

[0063] A more detailed description of the embodiments disclosed herein can be obtained by reference to the accompanying drawings. Some descriptive figures are merely schematic representations of the technologies and apparatus and therefore are no intended to describe relative size or dimensions of the components or assemblies thereof.

EXAMPLE 1

Simultaneous Assimilation of Organic Matter, Nutrients Recovery and Energy Production in Low Strength Wastewater

[0064] Wastewater with different composition and sources were fed to the system as summarized in Table 1. Feeds are based on two different domestic wastewater containing low (Experiments id 1, 2, 3) and high (Experiments id 4, 5, 6) ammonium concentration. The phototrophic culture was enriched in PPB treating domestic wastewater. In Experiments id 2 and 5, nutrients were removed by precipitation of phosphate with FeCl3 followed by ammonium stripping at pH 9. Experiments id 3 and 6 were carried out with a feed characterized by a COD/N/P ratio of 100/7.5/1.5, which is reported as optimum for PPB growth. The results are shown in FIGS. 5 and 6. These demonstrate that PPB biomass is highly-effective for raw domestic wastewater treatment, and assimilate soluble organics, nitrogen and phosphorus simultaneously. The results indicate that complete assimilation of organics and nutrients can be achieved in a single biological stage, where organics recirculation resulted from the PPB biomass hydrolysis step is an option. Under a suitable COD/N/P ratio, the system is described as in the FIG. 1. If organics recycle is needed to cope with optimum COD/N/P ratios for PPB growth, the system can be upgraded (see FIG. 3).

[0065] In the present example, reference is made to the elements of FIG. 3.

[0066] Stage 1: The anaerobic photobioreactor is a horizontal closed anaerobic ditch (301) fed by wastewater (307). Continuous flow is assessed by inlet and outlet flows (307, 308).

[0067] Stage 2: Phototrophic biomass is harvested from the anaerobic photobioreactor by separation systems (302). Purified water exits the system (309). Biomass is recycled through a biomass recirculation pipe (318), thereby maintaining a high biomass concentration inside the covered wastewater system (317) in the anaerobic ditch (301). Ideally, it is suitable up to around 10 gVSS/L.

[0068] Stage 3: Biomass collected in an outlet line (208, 310) is harvested and pre-treated (303) to (i) increase degradability and dewaterability, (ii) partially solubilize the organic matter and/or (iii) extract high-value products.

[0069] Stage 4: Solid/liquid separation (304) of pre-treated biomass (311), where solid/extracted follows downstream (312) and liquid is returned to the main line (314)

[0070] Stage 5: Biofuel (319) production of the collected phototrophic biomass through the anaerobic digester (305). After anaerobic digestion, nutrients are recovered as organic NPK fertilizer (313).

[0071] Stage 6: Nutrients recovery (N, P) in the return line (314) by crystallization of struvite (to fully recover P and partial N recovery) and electrodialysis (306) (to collect the remaining N as NH.sub.4.sup.+). Solid products are separated (316). Organic liquid phase is recycled into the main line (315) to maintain the COD/N/P ratios.

TABLE-US-00001 TABLE 1 Characteristics of wastewater treated in the anaerobic photobioreactors. Soluble organic matter as Total chemical Nitrogen Phosphorus suspended Experiment oxygen demand as NH.sub.4.sup.+ as PO.sub.4.sup.3 solids id (mg/L) (mgN/L) (mgP/L) (mg/L) pH 1 125.0 31.5 3.7 250.0 6.5 2 196.0 17.0 5.3 240.0 6.5 3 305.0 30.0 3.8 260.0 6.5 4 124.0 90.0 7.4 221.0 6.5 5 128.5 11.9 5.7 160.0 6.4 6 1039.0 92.0 7.9 262.0 6.6

EXAMPLE 2

Transformation of Organic Matter into High-Value Products in High Strength Wastewater

[0072] Alternatively, as stated in the description of Stage 3 in example 1, the process can be driven to separation and purification of valuable bioproducts downstream (instead, or in addition, to anaerobic digestion) (FIG. 4), as PHA, single-cell proteins, carotenoids or organic fertilizers. The biomass concentration in the photobioreactor in this case can be up to 10 g/L, therefore artificial illumination is strongly recommended during dark periods or during low sun irradiation. As well as, in this case Stage 5 in example 1 is modified. The sludge line (401) is submitted to extraction (402) of the bioproduct. Bioproduct and remaining biomass are separated by sedimentation or centrifugation (403). The concentrated stream (405) can be submitted to anaerobic digestion (as in the process 305), whereas the stream that contains bioproducts is fed to a subsequent purification step (404), where a purified marketable product is obtained (406).

[0073] The Project leading to this application has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 685793.