Mechanisms of persistence and impact of ordinary heterotrophic organisms in aerobic granular sludge.

The stability of granules, contaminant removal and microbial structure of an aerobic granular sludge (AGS) process were investigated with a focus on ordinary heterotrophic organisms (OHOs). Long-term stable granules and high removals of COD (97 %), NH4+ (98 %), P (85 %) and total N (77 %) were achieved. Sequencing analyses identified 6.6 % of phosphorus-accumulating organisms in the sludge, concordant with the observed bio-P removal capacity. However, OHOs were the most abundant bacteria in the sludge (70-93 %) without resulting in unstable aggregates. Under current dogmas of microbial competition in activated sludge, it seemed contradictory that OHOs could persist in the long term in the AGS where COD was depleted beginning in the anaerobic phase. Microbial analyses showed that OHOs could survive in granules by micropredation, proteolysis, fermentation and EPS consumption. Heterotrophic-nitrification/ aerobic-denitrification was an active pathway in the AGS. These findings contribute to a better understanding of microbial competition in AGS and its stability.

COD fractionation and biological treatability of mixed industrial wastewaters.

This study was conducted at a centralized wastewater treatment plant that receives discharges from nearly 160 industries. The chemical oxygen demand (COD) was fractionated for two objectives: delineation of the limits of the activated sludge process being used at the plant, and evaluation of the potential environmental impact of the treated effluent. Physico-chemical analyses, respirometric and biodegradation tests, as well as COD fractionation were carried out. Molasses-wastewaters were determined to be the major contribution to the plant. The influent was dark brown in color, with a relatively high content of both organics (2503 mg/L COD) and salts (5459 µS/cm conductivity), but a low biochemical oxygen demand (568 mg/L BOD(5)) and BOD(5)/COD ratio (0.24). The degradability of the organics was limited by the high content of inert soluble COD (S(I)). The COD fractionation pattern was 40-20-40% for S(I), X(I) (inerts) and S(H) (soluble hydrolyzable), respectively. More than 90% BOD(5) removal was obtained, which was sufficient for the plant to meet the national Standards. However, the effluent discharged into the river was intensely colored and polluted (>1000 mg/L COD, >5000 µS/cm), emphasizing the need for legislation regulating COD, color and salinity, and for upgraded treatment methods worldwide for molasses wastewaters.

A baseline assessment of hydrologic alteration degree for the Mexican catchments at gauged rivers (2016).

River regime has been modified in several freshwater bodies around the world. This alteration has led to species loss, water pollution, higher or lesser economic profits, changes in magnitude, timing, duration and rate change of flow, among others. Thus, hydrologic alteration assessment allows evaluating the regime parameters so that stakeholders, decision-makers, and dams managers may take efficient actions to mitigate or rehabilitate riparian ecosystems. In the present study, Hydrologic Alteration Indexes on Rivers (IAHRIS, for its acronym in Spanish) and the Mexican standard approach were considered to evaluate 1150 gauged catchments in Mexico and come up with an alteration baseline for 67.03% of the country surface. The comparison may assist stakeholders to propose potential changes in the Mexican standard approach. Results reveal that 232 analyzed catchments can be considered as non-altered according to IAHRIS. In stark contrast, there are 281 non-altered catchments in Mexico in agreement with the official standard approach. Altered catchments are mainly impacted by minimum flow metrics and connectivity discharge. Additionally, the correlation between alteration indexes and 5 socio-economic variables was checked to identify which variables may greatly impact hydrologic alteration evolution or mitigation. From the five selected variables, the Human Development Index is significatively correlated to extreme minimum metrics (p = 0.94) while the Gross Domestic Product to extreme maximum metrics (p = 0.90).

Initial-rate based method for estimating the maximum heterotrophic growth rate parameter (µHmax).

Currently, the method most used for measuring the maximum specific growth rate (µ(Hmax)) of heterotrophic biomass is by respirometry, using growth batch tests performed at high food/microorganism ratio. No other technique has been suggested, although the former approach was criticized for providing kinetic constants that could be unrepresentative of the original biomass. An alternative method (seed-increments) is proposed, which relies on measuring the initial rates of respiration (r(O2)(_ini)) at different seeding levels, in a single batch, and in the presence of excess readily biodegradable substrate (S(S)). The ASM1-based underlying equations were developed, which showed that µ(Hmax) could be estimated through the slope of the linear function of r(O2)(_ini)·(V(WW)+v(ML)) vs v(ML) (volume of mixed liquor inoculum); V(WW) represent the wastewater volume added. The procedure was tested, being easy to apply; the postulated linearity was constantly observed and the method is claimed to measure the characteristics of the biomass of interest.