Microalgae such as Chlorella vulgaris contain sufficient fatty acids to suggest their use as feedstocks for biodiesel production. Their capacity to remove nitrogen, phosphate, and other nutrients from a culture medium makes them a potentially useful element in urban wastewater treatment systems. A two-stage process was used to grow Chlorella vulgaris under mixotrophic and autotrophic conditions in artificial wastewater and urban wastewater media. Growth rate, nutrient removal, and lipids accumulation were quantified. Initially, the media were nitrogen-enriched (90 mg⁻¹; Stage I), and then nitrogen limited (30, 20, and 10 mg l⁻¹; Stage II). Growth was not inhibited under either of the culture conditions, and nitrogen uptake rates were above 90%. Total organic carbon removal was higher (56.2%–86%) under mixotrophic conditions than under photoautotrophic conditions (15.2%–69%). Lipids productivity was 2.7 times higher under mixotrophic conditions and nitrogen limitation than under photoautotrophic conditions and nitrogen limitation. Palmitic acid and linoleic acid accounted for 25.0% of total fatty acids contents, which is an adequate profile for biodiesel production. Culture of C. vulgaris in urban wastewater can improve the efficiency of nitrogen and total organic carbon removal, and water reuse, while simultaneously producing algal biomass with sufficient lipids content and an acceptable fatty acids profile for use as a biodiesel feedstock.

The objectives this study were to examine the integrated use of oil–coagulant for the direct extraction of coagulant from Moringa oleifera (MO) with 5% and 10% (NH₄)₂SO₄ extractor solution to harvest Scenedesmus obliquus cultivated in urban wastewater and to analyze the oil extracted from MO and S. obliquus. An average content of 0.47 g of coagulant and 0.5 g of oil per gram of MO was obtained. Highly efficient algal harvest, 80.33% and 72.13%, was achieved at a dose of 0.38 g L⁻¹ and pH 8–9 for 5% and 10% extractor solutions, respectively. For values above pH 9, the harvest efficiency decreases, producing a whitish water with 10% (NH₄)₂SO₄ solution. The oil profile (MO and S. obliquus) showed contents of SFA of 36.24–36.54%, monounsaturated fatty acids of 32.78–36.13%, and polyunsaturated fatty acids of 27.63–30.67%. The biodiesel obtained by S. obliquus and MO has poor cold flow properties, indicating possible applications limited to warm climates. For both biodiesels, good fuel ignition was observed according to the high cetane number and positive correlation with SFA and negative correlation with the degree of saturation. This supports the use of MO as a potentially harmless bioflocculant for microalgal harvest in wastewater, contributing to its treatment, and a possible source of low-cost biodiesel.

Sediment cores maintain a historical record of the various sources of polycyclic aromatic hydrocarbons (PAHs). In 2020, one sediment core was collected within the oyster farming area of the Pom–Atasta lagoon system and the Terminos lagoon. A total of 16 PAH compounds were analyzed to identify the historical patterns of PAH inputs and the relationship with sediment materials. The core was classified into three strata at depths of 0.0–0.2 m, 0.2–0.6 m, and 0.6–1.1 m, in which the high content of silt–sand, organic matter, and carbonates indicates a system of high energy and productivity. The hydrology and characteristics of the sediment suggest a free access of adsorbed PAHs to the study area, mainly of pyrolytic origin. The concentration of ∑PAHs decreases from the surface (527.0 ng g⁻¹ dw) to a greater depth (75.7 ng g⁻¹ dw), which corresponds to 60% of the HMW (high molecular weight) of the total PAHs as combustion products at low temperatures, while LWM-PAH (low molecular weight) inputs are from discharges of petroleum products. The core sediments showed a low probability of toxicity quotient of 9%. The analysis of the carcinogenic toxic equivalent (TEQ^carc) in each section of the core was variable, decreasing with the depth from 107.91 ng TEQ g⁻¹ dw to 57.65 ng TEQ g⁻¹ dw, with the compounds benzo(a)pyrene (53.55 ng TEQ g⁻¹ dw) and dibenzo(a,h) anthracene (29.2 ng TEQ^carc g⁻¹ dw) having the highest TEQ^carc. The anthropogenic activities around the study area may increase the carcinogenic and mutagenic risk to human health. However, in the present study, the low toxic carcinogenic equivalents (TEQ_BaP) and mutagenic equivalents (MEQ_BaP) indicate a low probability of sediment toxicity. The ecosystem could be under constant threat from increasing anthropogenic activity; therefore, monitoring programs for the conservation of these ecosystems and oyster farms should be considered.

Cheese consumption provides humans with minerals, proteins, carbohydrates, and vitamins. In Mexico, several cheese varieties are produced, each with its texture, scent, and flavor. The artisanal cheeses made in the states of Tabasco and Chiapas—including, among others, the varieties named crema (cream), doble crema (double cream), oaxaca, panela, fresco, bola, poro, cotija, and asadero—have a high demand in the domestic and foreign markets. The intensification of anthropic activity in these states causes an increased emission to the environment of contaminants like heavy metals, which could reach human foodstuffs through the food chains. In particular, heavy metal contents in cheeses consumed daily by these states’ local populations might represent a public health risk. Because of that, our objectives in this work were to determine the concentrations of lead, cadmium, nickel, copper, zinc, and iron in artisanal cheeses produced in the states of Tabasco and Chiapas and to determine the values of the hazard quotient (HQ), total hazard quotient (THQ), and cancer risk total (CRT) for adult and young men and women. The results of our analyses of cheese samples from the states of Tabasco and Chiapas showed that the average concentrations (mg kg⁻¹) of cadmium (0.0023 ± 0.002, 0.0023 ± 0.002 mg kg⁻¹, respectively, for each state), lead (0.0047 ± 0.00, 0.0051 ± 0.002), nickel (0.0039 ± 0.0046, 0.0031 ± 0.0039), copper (0.0199 ± 0.021, 0.0202 ± 0.022), zinc (0.1611 ± 0.18, 0.194 ± 0.21), and iron (61.84 ± 4.23, 65.76 ± 6.61 mg kg⁻¹), the first three values lower than the limits established by the FAO/WHO and Codex Alimentarius. The value of THQ that we obtained was less than one, and that of CRT was within the limits established by the US-EPA, which means that the consumption of artisanal cheeses from Tabasco and Chiapas by humans does not imply a risk of disease or cancer.

Wastewater treatment systems produce large volumes of sludge which is not used; its final disposal is in soil or landfill. This sludge represents a biomethane-energy alternative through anaerobic co-digestion, contributing to reducing the environmental impacts caused by their inadequate disposal. Biomethane production by the two-stage production method in batch digesters with pH and temperature control was evaluated by two qualities of waste-activated sludge (SLB₅₀ and SLB₉₀) and with a mixture of two co-substrates: cow manure (CEV₅₀ and CEV₉₀) and residual edible oil (CAV₅₀ and CAV₉₀). Bacteria in good-quality sludge (SLB₉₀) showed a faster adaptation of 2 days than those in low-quality sludge (SLB₅₀), with a 25-day lag phase. The highest CH₄ production was for SLB₉₀ (303.99 cm³ d⁻¹) compared to SLB₅₀ (4.33 cm³ d⁻¹). However, the cow manure–sludge mixture (CEV₉₀) contributed to the increased production of CH₄ (42,422.8 cm³ d⁻¹) compared to CEV₅₀ (12,881.45 cm³ CH₄ d⁻¹); for CAV₉₀ and CAV₅₀, these were 767.32 cm³ d⁻¹ and 211.42 cm³ d⁻¹, respectively. The addition of sludge co-substrates improves the nutrient balance and C/N ratio; consequently, methane production improves. This methodology could be integrated into concepts of the circular economy.