High-rate aerobic treatment of winery wastewater using bioreactors with free and immobilized activated sludge

Nitrate increases the capacity of an aerobic moving-bed biofilm reactor (MBBR) for winery wastewater treatment

We used bench-scale tests and mathematical modeling to explore chemical oxygen demand (COD) removal rates in a moving-bed biofilm reactor (MBBR) for winery wastewater treatment, using either urea or nitrate as a nitrogen source. With urea addition, the COD removal fluxes ranged from 34 to 45 gCOD/m2-d. However, when nitrate was added, fluxes increased up to 65 gCOD/m2-d, twice the amount reported for aerobic biofilms for winery wastewater treatment. A one-dimensional biofilm model, calibrated with data from respirometric tests, accurately captured the experimental results. Both experimental and modelling results suggest that nitrate significantly increased MBBR capacity by stimulating COD oxidation in the deeper, oxygen-limited regions of the biofilm. Our research suggests that the addition of nitrate, or other energetic and broadly used electron acceptors, may provide a cost-effective means of covering peak COD loads in biofilm processes for winery or another industrial wastewater treatment.

Biotreatment Potential and Microbial Communities in Aerobic Bioreactor Systems Treating Agro-Industrial Wastewaters

The thriving agro-industry sector accounts for an essential part of the global gross domestic product, as the need for food and feed production is rising. However, the industrial processing of agricultural products requires the use of water at all stages, which consequently leads to the production of vast amounts of effluents with diverse characteristics, which contain a significantly elevated organic content. This fact reinforces the need for action to control and minimize the environmental impact of the produced wastewater, and activated sludge systems constitute a highly reliable solution for its treatment. The current review offers novel insights on the efficiency of aerobic biosystems in the treatment of agro-industrial wastewaters and their ecology, with an additional focus on the biotechnological potential of the activated sludge of such wastewater treatment plants.

Immediate one-step lime precipitation process for the valorization of winery wastewater to agricultural purposes

The winery wastewater (WW) of the Village of Vidigueira, in south of Portugal, presented an acid pH (4.26 ± 0.029), a high content of chemical oxygen demand (COD = 3236 ± 30.43 mg L^-1), turbidity (160.0 ± 7.68 NTU), total P (155.5 ± 6.36 mg L^-1) K (100.5 mg L^-1), and low level of metals: Pb, Cd, Cu, Ni, Mn, Fe, Zn. The K and the total P content could make them attractive from an agricultural point of view. However, the high turbidity biochemical oxygen demand (BOD₅ = 1266.7 ± 208.7 mg O₂ L^-1) fecal coliforms (45 ± 29.8 ufc/100 mL) and toxicological total phenols 13.239 ± 3.007 mg galic acid L^-1 is the main limiting parameters. By using 5 g L^-1 of lime solution, the best reactional conditions are achieved: pH = 12 with a minimum volume of the produced sludge's, 33.5 ± 4.92 mL L^-1. These reactional conditions allow reaching high removal levels of BOD₅, turbidity, total P, and total phenols: 77.9, 98.7%, 87.1%, and 99.9%, respectively. Simultaneously, the fecal coliforms and Enterococcus are 100% eliminated. The precipitate obtained is rich in calcium (2.7891 ± 0.4350 mg Ca kg^-1) organic matter (10.05 ± 0.11%), P (895.0 ± 35.4 mg P₂O₅ kg^-1), and K (990.0 ± 84.9 mg K₂O kg^-1). During carbonatation reactions, the pH (7.46) and electrical conductivity (EC) (1.805 dS m^-1) decreased spontaneously while the Ca²⁺, K⁺, and F^- kept high: 426.53 mg L^-1, 240.53 mg L^-1, 176.03 mg L^-1, respectively.

Treatment of Winery Wastewater Using Bench-Scale Columns Simulating Vertical Flow Constructed Wetlands with Adsorption Media

Wastewater produced during the wine-making process often contains an order of magnitude greater chemical oxygen demand (COD) concentration than is typical of domestic wastewater. This waste stream is also highly variable in flow and composition due to the seasonality of wine-making. The recent growth of small-scale wineries in cold climates and increasing regulations present a need for low-cost, easily-operable treatment systems that do not require large amounts of land, yet maintain a high level of treatment in cool temperatures. This research investigates the use of a subsurface vertical flow constructed wetland (SVFCW) to treat winery wastewater. In this study, clinoptilolite, tire chips, and a nano-enhanced iron foam were used to enhance bench-scale gravel cells to adsorb ammonia, nitrate, and phosphorus, respectively. The treatment systems, without nitrogen adsorption media, performed well, with >99% removal of COD and 94% removal of total nitrogen. Treatment systems with the nitrogen adsorption media did not enhance nitrogen removal. Equilibrium was reached within two weeks of start-up, regardless of prior inoculation, which suggests that microbes present in the winery wastewater are sufficient for the start-up of the wastewater treatment system; therefore, the seasonality of winery wastewater production will not substantially impact treatment. Operating the treatment systems under cool temperatures did not significantly impact COD or total nitrogen removal. Further, the use of nano-enhanced iron foam exhibited 99.8% removal of phosphorus, which resulted in effluent concentrations that were below 0.102 mg/L P.

Biotreatment of Winery Wastewater Using a Hybrid System Combining Biological Trickling Filters and Constructed Wetlands

The objective of this work was to determine the ability of a pilot-scale hybrid system to treat real (non-synthetic) winery wastewater. The experimental treatment system consisted of two stages: An attached growth pilot-scale bioreactor (biological trickling filter with plastic support material) was initially used to remove a significant amount of dissolved chemical oxygen demand (d-COD) from winery wastewater, and then a pilot-scale, horizontal subsurface flow constructed wetland (CW) was examined as a post-treatment step for further d-COD removal. Results from the biofilter revealed that the recirculation rate of 1.0 L/min lead to higher d-COD removal rates than that of 0.5 L/min for all feed d-COD concentrations tested (3500, 7500, 9000 and 18,000 mg d-COD/L). Experiments in the CW were performed using feed d-COD concentrations of about 1500 mg/L (equivalent to biofilter effluent when initial filter feed d-COD concentrations are 18,000 mg/L). The wetland polishing stage managed to further remove d-COD and produced effluent concentrations below current legislation limits for safe disposal. Furthermore, the presence of zeolite in CW (one third of the length of CW) enhanced ammonium removal. The experimental results indicate that the combination of a biological trickling filter and a constructed wetland could effectively treat effluents originating from small wineries typical of the Mediterranean region.

Recovery of polyphenols onto porous carbons developed from exhausted grape pomace: A sustainable approach for the treatment of wine wastewaters

Removal of total polyphenols (TPP) is not only necessary as a pretreatment stepfor anaerobic digestion of wine wastewaters (WWW) but also the recovered polyphenols can be used as a dietary supplement. With a view to make the process sustainable, eco-efficient and cost effective, exhausted grape pomace (EGP) after the extraction of polyphenols was impregnated with ZnCl₂ (1:1.5) and further activated at 450 °C for 1 h under inert atmosphere. The GPAC (grape pomace activated carbon) thus developed exhibited well-developed porosity with a predominance of micropores, high surface area and selective surface binding sites. Batch adsorption conducted on diluted WWW revealed the better performance of GPAC (84.3% removal) as compared to EGP (48.5% removal) under similar conditions; with maximum adsorption taking place at pH 3.8. While pH studies indicated a possible electron-donor-acceptor mechanism in the binding of TPP, kinetic studies indicated that diffusion was mediated by the porosity in GPAC. Isotherm studies conducted on GPAC and commercial carbon (CAC) revealed multilayer binding under WWW while Langmuir model was operative under simulated conditions. Contrary to the better performance of CAC, the same for GPAC was comparable at higher dosage where >80%TPP was removed from undiluted WWW. The phenol adsorption capacity of GPAC from real (28.4 mg/g) and from simulated wastewater (142.6 mg/g) was higher as compared to other reported adsorbents. Desorption of TPP from loaded GPAC was maximum (∼91%) with 1:1 ethanol-water solvent. The results reveal a sustainable eco-friendly solution for valorisation of exhausted grape pomace for recovery of polyphenols from wine wastewater.

Environmental pollution and health hazards from distillery wastewater and treatment approaches to combat the environmental threats: A review

Distillery industries are the key contributor to the world's economy, but these are also one of the major sources of environmental pollution due to the discharge of a huge volume of dark colored wastewater. This dark colored wastewater contains very high biological oxygen demand, chemical oxygen demand, total solids, sulfate, phosphate, phenolics and various toxic metals. Distillery wastewater also contains a mixture of organic and inorganic pollutants such as melanoidins, di-n-octyl phthalate, di-butyl phthalate, benzenepropanoic acid and 2-hydroxysocaproic acid and toxic metals, which are well reported as genotoxic, carcinogenic, mutagenic and endocrine disrupting in nature. In aquatic resources, it causes serious environmental problems by reducing the penetration power of sunlight, photosynthetic activities and dissolved oxygen content. On other hand, in agricultural land, it causes inhibition of seed germination and depletion of vegetation by reducing the soil alkalinity and manganese availability, if discharged without adequate treatment. Thus, this review article provides a comprehensive knowledge on the distillery wastewater pollutants, various techniques used for their analysis as well as its toxicological effects on environments, human and animal health. In addition, various physico-chemicals, biological as well as emerging treatment methods have been also discussed for the protection of environment, human and animal health.

Mesophilic and thermophilic anaerobic co-digestion of winery wastewater sludge and wine lees: An integrated approach for sustainable wine production

In this work, winery wastes generated by a cellar producing approximately 300,000 hL of wine per year was monitored for a period of one year. On average, 196 L of wastewater, 0.1 kg of waste activated sludge (dry matter) and 1.6 kg of wine lees were produced per hectoliter of wine produced. Different winery wastes, deriving from different production steps, namely waste activated sludge from wastewater treatment and wine lees, were co-treated using an anaerobic digestion process. Testing was conducted on a pilot scale for both mesophilic and thermophilic conditions. The process was stable for a long period at 37 °C, with an average biogas production of 0.386 m³/kg COD_fed. On the other hand, for thermophilic conditions, volatile fatty acids accumulated in the reactor and the process failed after one hydraulic retention time (23 days). In order to fix the biological process, trace elements (iron, cobalt and nickel) were added to the feed of the thermophilic reactor. Metals augmentation improved process stability and yields at 55 °C. The pH ranged between 7.8 and 8.0, and specific gas production was 0.450 m³/kg COD_fed, which corresponded to dry matter and COD removals of 34% and 88%, respectively. Although the observed performances in terms of biogas production were good, the thermophilic process exhibited some limitations related to both the necessity of metals addition and the worse dewaterability properties. In fact, while the mesophilic digestates reached a good dewatering quality via the addition of 6.5 g of polymer per kg of dry matter, the required dosage for the thermophilic sludge was greater than 10 g/kg of dry matter.

Evaluation of a hybrid anaerobic biofilm reactor treating winery effluents and using grape stalks as biofilm carrier

Wine production processes generate large amount of both winery wastewater and solid wastes. Furthermore, working periods, volumes and pollution loads greatly vary over the year. Therefore, it is recommended to develop a low-cost treatment technology for the treatment of winery effluents taking into account the variation of the organic loading rate (OLR). Accordingly, we have investigated the sequential operation of an anaerobic biofilm reactor treating winery effluents and using grape stalks (GSs) as biofilm carrier with an OLR ranging from 0.65 to 27 gCOD/L/d. The result showed that, during the start-up with wastewater influent, the chemical oxygen demand (COD) removal rate ranged from 83% to 93% and was about 91% at the end of the start-up period that lasted for 40 days. After 3 months of inactivity period of the reactor (no influent feeding), we have succeeded in restarting-up the reactor in only 15 days with a COD removal of 82% and a low concentration of volatile fatty acids (1 g/L), which confirms the robustness of the reactor. As a consequence, GSs can be used as an efficient carrier support, allowing a fast reactor start-up, while the biofilm conserves its activity during a non-feeding period. The proposed hybrid reactor thus permits to treat both winery effluents and GSs.

Treatment of winery wastewater by physicochemical, biological and advanced processes: a review

Winery wastewater is a major waste stream resulting from numerous cleaning operations that occur during the production stages of wine. The resulting effluent contains various organic and inorganic contaminants and its environmental impact is notable, mainly due to its high organic/inorganic load, the large volumes produced and its seasonal variability. Several processes for the treatment of winery wastewater are currently available, but the development of alternative treatment methods is necessary in order to (i) maximize the efficiency and flexibility of the treatment process to meet the discharge requirements for winery effluents, and (ii) decrease both the environmental footprint, as well as the investment/operational costs of the process. This review, presents the state-of-the-art of the processes currently applied and/or tested for the treatment of winery wastewater, which were divided into five categories: i.e., physicochemical, biological, membrane filtration and separation, advanced oxidation processes, and combined biological and advanced oxidation processes. The advantages and disadvantages, as well as the main parameters/factors affecting the efficiency of winery wastewater treatment are discussed. Both bench- and pilot/industrial-scale processes have been considered for this review.

Microbial community structure at different fermentation stages of kutajarista, a herbal formulation

Kutajarista is an Ayurvedic fermented herbal formulation prescribed for gastrointestinal disorders. This herbal formulation undergoes a gradual fermentative process and takes around 2 months for production. In this study, microbial composition at initial stages of fermentation of Kutajarista was assessed by culture independent 16S rRNA gene clone library approach. Physicochemical changes were also compared at these stages of fermentation. High performance liquid chromatography-mass spectrometry analysis showed that Gallic acid, Ellagic acid, and its derivatives were the major chemical constituents recovered in this process. At 0 day of fermentation, Lactobacillus sp., Acinetobacter sp., Alcaligenes sp., and Methylobacterium sp. were recovered, but were not detected at 8 day of fermentation. Initially, microbial diversity increased after 8 days of fermentation with 11 operational taxonomic units (OTUs), which further decreased to 3 OTUs at 30 day of fermentation. Aeromonas sp., Pseudomonas sp., and Klebsiella sp. dominated till 30 day of fermentation. Predominance of γ- Proteobacteria and presence of gallolyl derivatives at the saturation stage of fermentation implies tannin degrading potential of these microbes. This is the first study to highlight the microbial role in an Ayurvedic herbal product fermentation.

Combination of Advanced Oxidation Processes and biological treatments for wastewater decontamination--a review

Nowadays there is a continuously increasing worldwide concern for development of alternative water reuse technologies, mainly focused on agriculture and industry. In this context, Advanced Oxidation Processes (AOPs) are considered a highly competitive water treatment technology for the removal of those organic pollutants not treatable by conventional techniques due to their high chemical stability and/or low biodegradability. Although chemical oxidation for complete mineralization is usually expensive, its combination with a biological treatment is widely reported to reduce operating costs. This paper reviews recent research combining AOPs (as a pre-treatment or post-treatment stage) and bioremediation technologies for the decontamination of a wide range of synthetic and real industrial wastewater. Special emphasis is also placed on recent studies and large-scale combination schemes developed in Mediterranean countries for non-biodegradable wastewater treatment and reuse. The main conclusions arrived at from the overall assessment of the literature are that more work needs to be done on degradation kinetics and reactor modeling of the combined process, and also dynamics of the initial attack on primary contaminants and intermediate species generation. Furthermore, better economic models must be developed to estimate how the cost of this combined process varies with specific industrial wastewater characteristics, the overall decontamination efficiency and the relative cost of the AOP versus biological treatment.

Granular activated carbon promoted ozonation of a food-processing secondary effluent

This paper reports on the application of a simultaneous combination of ozone and a granular activated carbon (O(3)/GAC) as a tertiary treatment of a wastewater generated from the activity of various food-processing industries. Prior to the O(3)/GAC treatment, the wastewater was subjected to conventional primary and secondary treatments in a full-scale wastewater treatment plant (WWTP). The effluent from the WWTP presented high organic load (COD>500 mg/l and TOC>150 mg/l), which could be much reduced by the O(3)/GAC treatment. Results from the O(3)/GAC experiments were compared with those obtained in single ozonation, single adsorption onto GAC and sequential O(3)-GAC adsorption experiments. While single processes and the sequential one showed limited capacity to remove organic matter for the food-processing effluent (COD removal <40%), the simultaneous O(3)/GAC process led to decreases of COD up to 82% at the conditions here applied. The combined process also improved the ozone consumption, which decreased from about 19 g O(3)/g TOC (single ozonation process) to 8.2-10.7 g O(3)/g TOC (O(3)/GAC process). The reusability of the GAC throughout a series of consecutive O(3)/GAC experiments was studied with no apparent loss of activity for a neutral GAC (PZC = 6.7) but for a basic GAC (PZC = 9.1).

Ozonation kinetics of winery wastewater in a pilot-scale bubble column reactor

The degradation of organic substances present in winery wastewater was studied in a pilot-scale, bubble column ozonation reactor. A steady reduction of chemical oxygen demand (COD) was observed under the action of ozone at the natural pH of the wastewater (pH 4). At alkaline and neutral pH the degradation rate was accelerated by the formation of radical species from the decomposition of ozone. Furthermore, the reaction of hydrogen peroxide (formed from natural organic matter in the wastewater) and ozone enhances the oxidation capacity of the ozonation process. The monitoring of pH, redox potential (ORP), UV absorbance (254 nm), polyphenol content and ozone consumption was correlated with the oxidation of the organic species in the water. The ozonation of winery wastewater in the bubble column was analysed in terms of a mole balance coupled with ozonation kinetics modeled by the two-film theory of mass transfer and chemical reaction. It was determined that the ozonation reaction can develop both in and across different kinetic regimes: fast, moderate and slow, depending on the experimental conditions. The dynamic change of the rate coefficient estimated by the model was correlated with changes in the water composition and oxidant species.

Gallic acid photochemical oxidation as a model compound of winery wastewaters

Winery wastewaters (WW) are characterized by their high organic load and by the presence of non-biodegradable compounds such as phenolic compounds. This study was undertaken to evaluate the capacity of different Advanced Oxidation Processes (AOP) combined with several radiation sources to degrade the phenolic compound Gallic Acid (GA). A toxicological assessment was also carried out to evaluate the subproduct's harmful effect generated during the most efficient AOP in the GA photoxidation. Through the course of the study it was verified that the UV radiation lamp TNN 15/32 showed the capacity to degrade 34.7% of GA, the UV radiation lamp TQ 150 achieved a value of 20.2% and the solar radiation presented only a value of 2.3% in 60 minutes. The combination of different advanced oxidation processes (Fenton's reagent, ferrioxalate and heterogeneous photocatalysis) were evaluated with the previously studied sources of radiation. From the experiments conducted it was possible to suggest that the AOP in combination with Fe(2 +) + H(2)O(2) + UV TNN 15/32 (photo-Fenton process) was the most efficient process thereby achieving the GA degradation value of 95.6% in 7.5 minutes and resulting in a total elimination of toxicity.

Production of fungal biomass protein using microfungi from winery wastewater treatment

This study was carried out to investigate the production of fungal biomass protein (FBP) in treatment of winery wastewater using microfungi. Three fungal strains, Trichoderma viride WEBL0702, Aspergillus niger WEBL0901 and Aspergillus oryzae WEBL0401, were selected in terms of microbial capability for FBP production and COD reduction. T. viride appeared to be the best strain for FBP production due to high productivity and less nitrogen requirement. More than 5 g/L of fungal biomass was produced in shake fermentation using T. viride without nitrogen addition, and by A. oryzae and A. niger with addition of 0.5-1.0 g/L (NH4)2SO4. The FBP production process corresponded to 84-90% COD reduction of winery wastewater. Fungal biomass contained approximately 36% protein produced by two Aspergillus strains, while biomass produced by T. viride consisted of 19.8% protein. Kinetic study indicated that maximum fungal cell growth could be achieved in 24h for T. viride and 48 h for A. oryzae and A. niger. Current results indicated that it could be feasible to develop a biotechnological treatment process integrated with FBP production from the winery waste streams.

Biological approaches for treatment of distillery wastewater: a review

Effluent originating from distilleries known as spent wash leads to extensive soil and water pollution. Elimination of pollutants and colour from distillery effluent is becoming increasingly important from environmental and aesthetic point of view. Stillage, fermenter and condenser cooling water and fermenter wastewater are the primary polluting streams of a typical distillery. Due to the large volumes of effluent and presence of certain recalcitrant compounds, the treatment of this stream is rather challenging by conventional methods. Therefore, to supplement the existing treatments, a number of studies encompassing physico-chemical and biological treatments have been conducted. This review presents an account of the problem and the description of colour causing components in distillery wastewater and a detailed review of existing biological approaches. Further, the studies dealing with pure cultures such as bacterial, fungal, algal and plant based systems have also been incorporated. Also, the roles of microbial enzymes in the decolourization process have been discussed to develop a better understanding of the phenomenon.

Factorial experimental design of winery wastewaters treatment by heterogeneous photo-Fenton process

Winery wastewaters are difficult to treat by conventional biological processes because they are seasonal and experience a substantial flow variations. Photocatalytic advanced oxidation is a promising technology for wastewaters containing high amounts of organic matter. In this work, the photo-Fenton process in heterogeneous phase is presented as an alternative methodology for the treatment of winery wastewaters. As a consequence of the great number of existing variables, an experimental design methodology has been used in order to study the influence and interaction of various variables and to obtain a reduced empirical model which describes the organic matter degradation process. Applying photo-Fenton treatment in heterogeneous phase under energetic conditions for synthetic samples simulating winery wastewaters results in purification levels of up to 50% (measured as total organic carbon). Different reduced models are obtained and their utilization depends mainly on the degree of degradation of organic matter required.

Beta-glucan production by Botryosphaeria rhodina in different bench-top bioreactors

AIMS

Evaluation of the technical feasibility of transferring beta-glucan production by Botryosphaeria rhodina DABAC-P82 from shaken flasks to bench-top bioreactors.

METHODS AND RESULTS

Three different bioreactors were used: 3 l stirred tank reactor (STR-1) equipped with two different six-blade turbines; STR as above but equipped with a three-blade marine propeller plus draft-tube (STR-2); 2 l air-lift column reactor (ALR) equipped with an external loop. STR-1, tested at three different stirrer speeds (300, 500 and 700 rev min(-1)) appeared to be less suitable for beta-glucan production by the fungus, being maximum production (19.4 g l(-1)), productivity (0.42 g l(-1) h(-1)) and yield (0.48 g g(-1) of glucose consumed) markedly lower than those obtained in shaken culture (29.7 g l(-1), 1.23 g l(-1) h(-1) and 0.61 g g(-1), respectively). Better performances were obtained with both STR-2 and ALR. With the latter, in particular, the increase of production was accompanied by reduced fermentation time (25.7 g l(-1) after only 22 h); productivity and yield were highest (1.17 g l(-1) h(-1) and 0.62 g g(-1) of glucose consumed, respectively).

CONCLUSION

Using an air-lift reactor with external loop, the scaling up from shaken flasks to bench-top bioreactor of the beta-glucan production by B. rhodina DABAC-P82 is technically feasible.

SIGNIFICANCE AND IMPACT OF THE STUDY

Although culture conditions are still to be optimized, the results obtained using the ARL are highly promising.

Microbial characterisation of activated sludge in jet-loop bioreactors treating winery wastewaters

Jet-loop reactors (JLR) used as biological waste treatment processes introduce an additional selective pressure on the natural microbial flora of the incoming effluent. Several high-performing microbial inocula were tested for winery wastewater treatment and the microbial composition was analysed. A microbial consortium was enriched and selected for use with a new type of aerobic JLR. The reactor was operated continuously for more than 1 year using winery wastewaters collected in different seasons. Chemical oxygen demand (COD) removal efficiency was on average greater than 80%, with retention times of 0.8-1 day. Microbial populations were sampled for characterisation after 6 months and at the end of the study. Isolates were identified at genus and/or species level. Almost all isolates belonged to the genera Pseudomonas and Bacillus. Saccharomyces cerevisiae was also found but no filamentous fungi. These results show that a highly adapted population develops in JLRs treating winery effluents as compared to other bioreactors. Aerobic JLRs impose a stringent selective criterion on the composition of the microbial biomass.

Microbiology of a biological contactor for winery wastewater treatment

Winery wastewaters are characterised by large seasonal fluctuations in volume and composition and are often discarded with little or no treatment. A rotating biological contactor (RBC) was used to investigate microorganisms associated with the biological treatment of winery wastewater. Extensive biofilms developed on the RBC discs and contained a number of yeast and bacterial species that displayed a dynamic population shift during the evaluation period. This suggested that the naturally occurring microorganisms were able to form a stable biofilm and also reduce the chemical oxygen demand (COD) of winery wastewater (on average 43% with a retention time of 1h). One of the yeast isolates, MEA 5, was able to reduce the COD of synthetic wastewater by 95% and 46% within 24h under aerated and non-aerated conditions, respectively. The yeast isolates could therefore play an important role in the degradation of organic compounds under aerobic conditions, such as those associated with an RBC.