Segregation of solid waste from a fish-processing industry : a sustainable action

Segregation techniques represent a sustainable alternative to minimize wastes of raw material in processing industries. This study considered the premise; its purpose was to use segregation techniques to determine the theoretical removal rate of solid compounds present in processing effluents, in order to support the sustainable development of the fish industry. The removal rates obtained for different treatments were evaluated for the parameters: total solids, organic matter and oils and greases, and the efficiency of the segregation of the effluent streams in the different stages of fish processing was evaluated through descriptive statistical analysis. The segregation recovered from 31% to 70% of total solids; from 15% to 97.50% of organic matter, and from 10% to 63% of oils and greases. These results indicates that the raw material can be used in new products, leading to reduced final-effluent concentration.


INTRODUCTION
Food waste is a current reality, from initial processing through distribution to the final consumer, part of the raw material that reaches the food-processing industries is wasted.This factor contributes to the generation of liquid and solid waste (ONU, 2012), which reduces food availability and increases the polluting potential of the food industry.The fish-processing industry is considered to be one of the industries that generate waste with maximum load (Chowdhury et al., 2010;Cristovão et al., 2012;2015).
The effluent generated during the processing of this product includes soluble, colloidal and particulate forms of organic contaminants (Chowdhury et al., 2010), including proteins, nutrients, oils and greases (Muthukumaran and Baskaran, 2013).The main solid waste produced consists of scales, meat, bones, cartilage and viscera (Anh et al., 2011).In processing, the disposal of these residues is between 50 and 70% of the processed fish Hernández et al., 2013;Feltes et al., 2010, Herpandi et al., 2011;Monteiro, 2013;Rustad et al., 2011;Silva et al., 2014).Of this volume of generated waste, approximately half is equivalent to organic materials (Bugalo et al., 2012), and lacks a suitable site for disposal (Morais et al., 2013).However, due to the high organic load, the potential pollutant of the final effluent is high, and should be considered (Cosmann et al., 2009;Hernández et al., 2013;Bugalo et al., 2012).
However, the search for sustainability generates goals such as the reduction of waste and the search for an increase in the efficiency of the production chain (Love et al., 2015;ONU, 2012), food availability and natural resources.Also, cleaner production, such as reuse, recycling, and other green technologies is encouraged instead of using the disposal and the endof-pipe treatment for waste management (Wu et al., 2013).This necessitates the search for alternatives applicable to food processing, which reduce the volume of the waste generated, as well as economic valuation for the by-products produced (Lago, 2015;Lopes et al., 2015;FAO, 2014).
In this scenario, segregation presents itself as a management option for the waste generated, and can be applied during the processing of the food or later, in the pre-treatment phase, before the processing effluent comes into contact with the effluent generated in the pretreatment phase, in order to reduce the risk of contamination, minimize the effluent flow, and reduce the cost of treatment and final disposal of the waste (Johanson, 2014;Alonso et al., 2010;Lopes et al., 2015;Mittal, 2006).Segregation is accomplished by adopting several techniques including: decantation, sieving, and filtration, which are unitary operations and can be used to recover part of the solid waste present in the effluent, the presence of which increases the pollutant load and requires more complexes treatments (Bezama et al., 2012).
The segregation depends on the characteristics of the constituent material.Thus, for example, different operations are required when the sedimentation, sedimentation capacity and density difference of the material are preponderant, so that the process takes place efficiently.For sieving and filtration, which use the same principle of particle separation, one should consider the size of the material to be separated (Johanson, 2014;Sutherland, 2011;2013).It is necessary to study the fish production process and the effluent generated in the different steps.The implementation of segregation depends on the type and volume of effluent produced and the chief generating points.This study analyzed the theoretical efficiency of segregation applied to the different streams of effluents produced in a fish warehouse to reduce solids, organic matter and oils and greases, in order to support the sustainable development for the fishprocessing industry.

Processing of raw material
The study was carried out in a fish warehouse located in the northern region of Brazil, which processes 1687.50 kg/month of fish.The species processed were Colossoma macropomumi (tambaqui), Brycon cephalus (matrinxã), Pseudoplatysto macorruscans (pintado) and Leporinus freiderici (piau).The raw material was processed through evisceration and cooling in four steps: initial (I); Evisceration (II) cooling (III) and global (IV) (Figure 1).Step I was configured for receiving, weighing, sanitizing and transporting the raw material to the subsequent step, the processing.Step I was therefore characterized by the generation of liquid effluent with the presence of pieces of fish, oils and greases.Step II was evisceration, which employs a cutting or abdominal incision table and subsequent evisceration.The fish was placed on the evisceration table, the viscera was manually removed, the product weighed, cleaned, stored and subsequent routed to refrigeration.This stage is characterized by the generation of liquid effluent with pieces of fish, oils and greases, viscera, and blood.
Step III, the cooling room, is the storage location for the product and the waste.The product was conditioned and cooled in monoblocs until distribution to market and the waste goes to the treatment plant.This step was characterized by the washing of the monoblocs, with the generation of liquid effluent accompanied by blood and residues of the material used in the cleaning of the place.
Step IV corresponds to the effluent created during fish processing and monobloc washing.

Sampling points, effluent characterization and evaluation of effluent segregation
Effluent samples were collected at the following points: I (Initial step), after the washing cylinder; II (Processing step), after the fish evisceration table; III (Cooling step); and IV, after packing the product in refrigerated space monoblocs.The samples were taken at the effluent junction site (from processing and administrative area).
The analysis of the effluent was carried out as follows: total solids (ST) Ref. 2540-G Total, fixed, and volatile solids in solid and semisolid samples), biochemical oxygen demand (BOD), technique Ref. 5210 B. 5-Day BOD Test), chemical oxygen demand (COD) Ref. 5220 Closed reflux titrimetal method), and oils and greases (Ref.5520-B Partition gravimetric method).The analyses were performed as described in the Standard methods for the examination of water and wastewater (APHA, 2005).

The segregation of effluent streams
In order to determine the rate of removal of the pollutants from the application of segregation in the effluent streams of each of the processing stages, the percentages of removal were determined for the studied compounds (total solids, organic matter, and oils and greases) obtained theoretically when employed in different unit operations and processes, namely: -the percentage of theoretical removal for the separation of total solids was determined by the following techniques: screening; screen combined with filter and catch basin; screen, filter and catch basin with removal; screening with microfiltration, ultrafiltration, nanofiltration and reverse osmosis; flotation by dissolved air.
-the following techniques were used to determine the segregation of organic matter: screens; rotating filter; rotary sieve; ultrafiltration; prefiltration conjugated to nanofiltration.
-for the segregation of oils and greases, the membrane filtration processes associated with electrocoagulation were studied, specified by dynamic membrane and electrocoagulation, ceramic and electrocoagulation membrane, ceramic membrane, and dynamic membrane.
To determine the efficiency of the application of the segregation, descriptive statistical analysis was used, adopting the calculation of summary measures, taking into account the nature of the variables involved.For the inferential analysis of the results, parametric tests were used, taking into account the nature of the distributions of the values or the variability of the measurements made.This was accomplished using the Microsoft Office Excel 2007 statistical package.

RESULTS AND DISCUSSION
For the characterization of the effluent from Steps I, II, III and IV of the fish processing, the total solid parameters were analyzed, adopting the parameters: total solids, organic matter (BOD5, 20, and COD) and oils and greases.For the total solids (Figure 2a) the following average concentrations were found: 1740 g L -1 (Step I); 2714 g L -1 (Step II); 444.1 g L -1 (Step III), and 2094 g L -1 (Step IV).The concentrations were similar to those found in other studies (Chowdhury et al., 2010;Garde, 2011).They presented the typical characteristics of the processing in the industry, whose final product is only gutted fish, not filleting, or preserving, for example, that increase solids in effluents.
Using the COD test, the organic matter showed a mean concentration of 1446 g L -1 in Stage I, 1811 g L -1 in Stage II, 167.6 g L -1 in Stage III and 1592 g L -1 in Stage IV (Figure 2b).A high content of organic matter was found in the steps that correspond to the processing itself and in the global effluent, due to the added load which originated in the processing.This is similar to the findings of other studies (Alexandre et al., 2014;Cristovão et al., 2012;2015;Chowdhury et al., 2010;Garde, 2011;Anh, 2011;Queiroz et al., 2013).
When analyzing the BOD, the results were compatible with those obtained in the COD analysis and the concentrations were close to those obtained in other fish processing industries (Alexandre et al., 2014;Cristovão et al., 2012;2015;Chowdhury et al., 2010;Garde, 2011;Anh, 2011;Queiroz et al., 2013).The mean BOD concentrations of 699.1 g L -1 in Step I; Rev. Ambient.Água vol.13 n.2, e2155 -Taubaté 2018 908 g L -1 in Step II; 80.3 g L -1 , in Step III and 742.5 g L -1 in Step IV were found in this study (Figure 2c).The highest concentration of organic matter in Step II was associated with evisceration and hygiene activities, which added solid waste to the effluent collection network, such as viscera, the residue most generated in the warehouse studied, besides blood and pieces of the fish, increasing the biodegradability of the effluent.It is observed that the reduction of the organic matter content is primordial, indicative of the necessity of the segregation of this effluent.
For the oils and greases, a concentration of 0.172 g L -1 was obtained in Stage I, 0.837 g L -1 in Stage II, 0.0316 g L -1 in Stage III and 0.701 g L -1 in Stage IV (Figure 2d).All steps studied presented upper and lower limits in relation to the quality standard recommended by the legislation CONAMA Resolution 357/2005 and complementary 430/2011 (CONAMA, 2006;2011).As expected, Step II presents a higher concentration among the other stages studied due to the characteristics of the residues generated in this as a result of evisceration.This parameter differs greatly from industry to industry, since those that process preserves add oil to the product, so these data may be divergent from study to study, such as those performed by Mosquera-Corral et al. (2001), Cristovão et al. (2012;2015), whose concentrations were between 156 g L -1 and 2841 g L -1 of oils and greases.Based on the characterization of the effluent generated in the fish processing industry, a study can determine the concentrations of the parameters of interest.When applied to the segregation of effluent streams, this would aid in verifying the efficiency in reducing the concentration of these in the final effluent and in evaluating the possibility of recovery of coproducts.This is especially important because the concentration of pollutants in effluent is equivalent to the concentration of final waste from the processing industry, even for different raw materials such as fish, seafood and crustaceans (Alexandre et al., 2014;Anh et al., 2011).
The implementation of technical segregation minimizes the final concentration of the pollutant, facilitating the operations involved in the treatment and also allowing the use of co-products, as previously mentioned.The theoretical percentages of removal obtained from the use of different segregation techniques for the studied compounds (total solids, organic matter, oils and greases) (Table 1) were used in the processing steps (I, III, II and IV) of the industry under study.The results when using the theoretical percentages of removal, related to the total solids found in the effluents from Steps I, II, III and IV according to the segregation techniques adopted.When simplified techniques are used, the reduction is from 25 to 60% (Figure 3a and  b).However, reductions of up to 90% are achieved when the techniques are associated (Figure 3c).
For removal of organic matter, the highest theoretical percentages were associated with segregation techniques that operate through nanofiltration, dissolved air flotation, coagulationflotation and reverse osmosis (Figure 4).These segregation techniques were able to remove up to 97.50% of the organic matter (Figure 4), that results in a quality effluent to be directly released into a water body, or to be reused or recycled in the processing, according to Brazilian legislation in force (Resolution CONAMA 430/2011(CONAMA, 2011) and Resolution 54/2005 of the CNRH ( 2006).If the effluent from segregation is treated, a simplified system Rev. Ambient.Água vol.13 n.2, e2155 -Taubaté 2018 will suffice.When the less efficient techniques are adopted, such as screens, it is still possible to achieve a 25 to 60% reduction, which is important, when the compound is to be minimized, as organic matter considered as one of the big problems for the treatment of effluents.In general, the rate of removal of organic matter obtained when using screens was 25% to 60% (Figure 4a); rotary filters reached 15% (Figure 4b); rotating sieve reached 25% (Figure 4c); nanofiltration conjugated prefiltration reached 56% (Figure 4d); ultrafiltration reached 30% to 36% (Figure 4e); nanofiltration reached 60% to 80% (Figure 4f); dissolved air flotation reached 30% to 90% (Figure 4g); coagulation-flotation reached 90% (Figure 4h), and reverse osmosis 97.50% (Figure 4i).
Oils and greases must be removed from fish-processing effluents, because they interfere with oxygen transfer, and cause operational problems in treatment systems (Alexandre et al., 2014); but primary treatments are sufficient to remove this contaminant, at least in part (Muthukumaran and Baskaran, 2013).In this study, when used at the theoretical removal rate achieved by the segregation techniques studied (Figure 5), it was possible to reduce up to 65% of the initial concentration when membrane filtration associated with electrocoagulation was adopted (Figure 5a).
Flotation reached from 37% to 63% removal for the parameter (Figure 5e).Due to the importance of this parameter, even the lowest rates of reduction contribute to both effluent treatment and disposal.It is also important to consider the possibility that this compound can be used to produce biofuels (Jayasinghe and Hawboldt, 2012;Alonso et al., 2010;Adeoti and Hawboldt, 2014).Analyzing the results, segregation proved to be an efficient technique to minimize concentrations of the studied compounds: total solids, organic matter and oils and greases (Table 2).However, it does not exempt the final treatment effluent.The COD/BOD ratio below 2.5 indicates biodegradable matter, so there is an indication that it requires treatment for stabilization.

CONCLUSION
The segregation techniques studied showed that, for the effluent under study, higher rates of removal of solids, organic matter and oils and greases were reached when conjugated processes were adopted.The result is a final effluent with less polluting potential, thus requiring a more-simplified treatment.
Segregation of total solids, organic matter and oils and greases showed a better result in Step II (evisceration step) as a function of the solid waste load, such as pieces of fish, viscera and blood generated during processing.
Due to the low load of total solids, organic matter and oils and greases of Stage III (monobloc wash), the implementation of segregation techniques would result in an effluent in accordance with Brazilian legislation in force.
The introduction of segregation processes in the effluent streams not only allows the production of a better final effluent, but also the reduction of by-product loss.

Figure 1 .
Figure 1.Fish processing in the refrigerator under study with indication of collection points of effluent samples for physical and chemical characterization.

Figure 2 .
Figure 2. Concentration of total solids (a), Chemical demand for oxygen (b), biochemical oxygen demand (c), and oils and greases (d) found in the effluent generated during fish processing.

Figure 3 .
Figure 3. Estimation of total solids concentration in the processing effluent after application of segregation techniques.Legends: (a) Screening; (b) Screen; (c) Screen combined with filter and catch basin; (d) Dissolved air flotation (DAF).

Figure 5 .
Figure 5. Oils and greases in mg/L per step after application of the rates of removal by segregation technique present in the effluent in fish-processing industry.Legend: (a) Membrane filtration associated with electrocoagulation; (B) Ceramic membrane and electrocoagulation; (C) Ceramic membrane; (D) Dynamic membrane; (E) Flotation; (F) Screen.

Table 1 .
Segregation techniques and percentages of removal achieved for the compounds studied.

Table 2 .
Methods of segregation employed in-fish processing industry for the removal of total solids, organic matter and oils and greases, and maximum efficiency when applied in the following processing Steps: I (Initial stage) after the washing cylinder; II (Processing stage), after the fish-evisceration table; III (Cooling stage), after packing the product in monoblocs in refrigerated space; and IV (Processing effluent stage and administrative area).