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The state of Minas Gerais is one of Brazil's largest animal protein producers, and its slaughterhouses generate highly polluting wastewater, which needs to be treated for discharge or reuse. As a novelty, this review article focused on assessing the characteristics and methods to treat wastewater from slaughterhouses in the state of Minas Gerais, and verifying its compliance with environmental regulatory agencies. The aim was to present data that helps to better manage this residue in other Brazilian states and countries. By analyzing the literature data, it was found that raw slaughterhouse wastewater (SWW) showed a high concentration of organic matter. For most SWW, the BOD 5 /COD ratio was above 0.4, which implies that it can be treated biologically. Generally, treated wastewater was in accordance with legal discharge standards, considering COD and BOD 5 removals above 70% and 75%, respectively. It was found that wastewater treatment plants (WWTPs) consisted of some type of pretreatment (screens, grease traps) to remove coarse solids and fatty material, eventually followed by a flotation step and finally by biological processes, mostly anaerobic and/or aerated (or facultative) ponds. However, the absence of an aerobic process at the end of the treatment in some WWTPs, in addition to a system allowing better removal of biological flocs, might be the reason for ammoniacal nitrogen and suspended solids values being above the allowed maximum in treated wastewater, respectively. Besides the discharge into water bodies, it was verified that fertigation using treated SWW is very common in the state of Minas Gerais. [Display omitted] • Slaughterhouse wastewater has a high concentration of organic matter and nutrients. • Preliminary and primary treatments consist of screening and flotation, respectively. • Anaerobic followed by aerobic ponds is the most commonly used biological treatment. • Ammonia and suspended solids were above the maximum allowed in treated wastewater. • Fertigation has been verified for disposing of treated wastewater in Minas Gerais. [ABSTRACT FROM AUTHOR]

Besides reducing the sewage organic and nutrient load, microalgae-based wastewater treatments promote the recovery of important natural resources, such as N and P, which can be used for biofuels and animal feed production. In this context, the present study proposes a treatment system based on a circular economy and resource recovery of waste streams: an up-flow anaerobic reactor (UASB, widely used in developing countries such as Brazil) followed by high-rate algae ponds (HRAPs). Geographic Information Systems tools were used to select suitable areas for allocating the proposed system in Minas Gerais (Brazil). Two regions showed excellent suitability for allocating the UASB + HRAP system, with more than 70% coverage each. These areas cover 59 municipalities, with a production capacity of 43,565 m³/day of raw sewage, a volume that, after treatment, can be used for crop irrigation and fish farming. In addition, municipalities can produce 6621.9 kg/day of microalgae biomass. This biomass can generate 13.96 MWh/day of electrical energy, 1316.7 kg/day of nutrients for animal feed, 3.97 kg of β-carotene, 2576.3 kg of biodiesel, 132.4 kg of Omega-3, 198.7 kg of glycerol or 1125.72 kg of ethanol. Productivities were calculated from three by-product valorization routes of the suggested system: energy, agriculture, and high-value products. The proposed system improves current wastewater treatment standards in the selected regions, with the potential to generate valuable resources compatible with attractive economic activities from these areas. [Display omitted] • Norte de Minas and Central Mineira have greater suitability for the proposed system. • Main resource recovery routes are anaerobic digestion, agriculture and biorefinery. • The proposed treatment system can produce energy, animal feed, ethanol and biodiesel. • Areas can produce 6621.9 kg day-1 of algal biomass from 43,565 m³ day-1 of sewage. • For animal feed, recovery potential of 1316.67 kg day-1 of algal biomass. [ABSTRACT FROM AUTHOR]