The aim of this study was to find out if nejayote produced at household level in Guatemala represents a threat to aquatic ecosystems and, if so, propose sustainable processing, reuse and disposal methods. First, all aspects related to nejayote production were explored. This study presents combined results from literature study on corn consumption and Guatemalan demography, a survey to Guatemalan women of all ethnical groups, nixtamalization replica and solids removal experiments and laboratory analysis. Findings indicate that the source of nejayote are approximate 600 000 tones of corn nixtamalized yearly by Mayan women from the rural areas of Guatemala to prepare tortillas for a population of about 5 000 000. From this activity approximately 300 000 tones of concentrated nejayote are produced and 800 000 tones of water are polluted yearly. Approximate 63% of these volumes are discharged into water ecosystems without treatment due to lack of knowledge of its potential negative impact or reuse properties. The study was done on nejayote produced at national level, but the isolation of the Mayan population within less than 20% of the national territory, suggests higher punctuality of nejayote discharges. Chemical and physical analyses made to samples from the nixtamalization replica confirmed its similarity to industrial nejayote, which has proven to be highly pollutant due to high content of organic matter from corn grain pericarp and germ. Concentrations ranges from 200 to 300 ppm of nitrogen, 160 to 190 ppm of phosphorus and 25 000 to 28 000 ppm of organic matter make it a potential fertilizer or soil conditioner. Studies indicate that it can be safely reused as supplementary food for chickens and pigs, to prepare additional corn based foods for humans or it could be safely discharged into ponds, wetlands or pits to minimize any environmental impact. Although findings point to nejayote as a potential aquatic ecosystem pollutant, this depends on the capacity of the specific recipient aquatic ecosystem to adsorb and process the nutrients and on the volumes and concentration of nutrients of the nejayote discharged that might vary from household to household. However, the nutrient rich nejayote can be seen as a potential resource, instead of a pollutant, to improve the nutritional, social and economical conditions of the Mayan populations. Specially women, an isolated segment of society that lacks opportunities and who, according to findings of this study, start processing corn into tortillas from early childhood and continue throughout all their lifetime without any benefit on return.

This thesis presents an assessment of the availability and quality of biomass from the wastewaters in a traditional corn mill in Mexico City for biogas production. To date, these wastewaters (called nejayote) are discharged untreated to the sewer with a chemical composition that surpasses the maximum permissible levels of pollutants established in the Official Mexican Standards (NOMs). From the study case four scenarios were proposed to tackle this problem: 1) separate the suspended solids (SS) by sedimentation in order to reduce the organic content of nejayote, 2) recover a protein-rich microbial biomass for animal feed through the aerobic treatment of these wastewaters, 3) produce biogas to cover part of the energy demand of the corn mill under study, and 4) switch to the alkaline extrusion of corn as an alternative the traditional corn-cooking technique known as nixtamalization. Despite their environmental benefits, none of the proposed scenarios offer, separately, the economic incentives to change the business as usual in this traditional corn mill. Yet, biogas production can be combined with other alternatives like the alkaline extrusion of corn in a two-stage technological package. This processing technology would completely eliminate nejayote while preserving the nutritive value of the nixtamal dough and most importantly, the organoleptic uniqueness of the traditionally-made tortillas.