SANASA Capivari II - the first full-scale municipal membrane bioreactor in Latin America.

The macro region of Campinas (Brazil) is rapidly evolving with new housing developments and industries, creating the challenge of finding new ways to treat wastewater to a quality that can be reused in order to overcome water scarcity problems. To address this challenge, SANASA (a publicly owned water and wastewater concessionaire from Campinas) has recently constructed the 'EPAR (Water Reuse Production Plant) Capivari II' using the GE ZeeWeed 500D(®) ultrafiltration membrane system. This is the first large-scale membrane bioreactor (MBR) system in Latin America with biological tertiary treatment capability (nitrogen and phosphorus removal), being able to treat an average flow of 182 L/s in its first phase of construction. The filtration system is composed of three membrane trains with more than 36,000 m(2) of total membrane filtration area. The membrane bioreactor (MBR) plant was commissioned in April 2012 and the permeate quality has exceeded expectations. Chemical oxygen demand (COD) removal rates are around and above 97% on a consistent basis, with biochemical oxygen demand (BOD5) and NH3 (ammonia) concentrations at very low levels, and turbidity lower than 0.3 nephelometric turbidity unit (NTU). Treated effluent is sent to a water reuse accumulation tank (from where will be distributed as reuse water), and the excess is discharged into the Capivari River.

Assessment of compatible solutes to overcome salinity stress in thermophilic (55 degrees C) methanol-fed sulfate reducing granular sludges.

High NaCl concentrations (25 g x L(-1)) considerably decreased the methanol depletion rates for sludges harvested from two lab-scale sulfate reducing UASB reactors. In addition, 25 gNaCl x L(-1) strongly affected the fate of methanol degradation, with clear increase in the acetate production at the expense of sulfide and methane production. The addition of different osmoprotectants, viz. glutamate, betaine, ectoine, choline, a mixture of compatible solutes and K+ and Mg2+, slightly increased methanol depletion rates for UASB reactors sludges. However, the acceleration in the methanol uptake rate favored the homoacetogenic bacteria, as the methanol breakdown was steered to the formation of acetate without increasing sulfate reduction and methane production rates. Thus, the compatible solutes used in this work were not effective as osmoprotectants to alleviate the acute NaCl toxicity on sulfate reducing granular sludges developed in methanol degrading thermophilic (55 degrees C) UASB reactors.

Sulfidogenic volatile fatty acid degradation in a baffled reactor.

The effect of staging the sludge bed on volatile fatty acid degradation by sulfidogenic reactors was evaluated in a baffled reactor. In a 5.4 l baffled reactor, containing three equal compartments, a volatile fatty acid (VFA) mixture (acetate:propionate:butyrate ratio 1:2:2 on COD basis; pH 8) was treated under mesophilic (30 degrees C) and sulfidogenic (COD:SO4(2-) ratio: 0.5) conditions for 38 days. At a specific sludge loading rate of 0.50 g COD.gVSS(-1) x d(-1), a COD and sulfate removal of 85% and 30%, respectively, was obtained. In the baffled reactor, staging of the sulfidogenic VFA degradation occurred. Propionate and butyrate were mainly degraded in the first compartment. Their degradation was incomplete, resulting in elevated acetate concentrations in compartment I. In the second and third compartment of the baffled reactor, a net degradation of acetate took place. Acetate was the sole substrate present in compartment III and residual acetate concentrations of about 200 mg/l were present in the effluent at a specific sludge loading of 0.50 g COD x gVSS(-1) x d(-1). Sludges with different maximum specific VFA and acetate degrading activities developed in the first and second compartment. These maximal specific activities were almost equal for sludge present in compartment II and III.

Long-term adaptation of methanol-fed thermophilic (55 degrees C) sulfate-reducing reactors to NaCl.

A laboratory-scale upflow anaerobic sludge bed (UASB) reactor was operated during 273 days at increasing NaCl concentrations (0.5-12.5 g NaCl l(-1)) to assess whether the stepwise addition of the salt NaCl results in the acclimation of that sludge. The 6.5-l thermophilic (55 degrees C), sulfidogenic [a chemical oxygen demand (COD) to SO4(2-) ratio of 0.5] UASB reactor operated at an organic loading rate of 5 g COD l(-1) day(-1), a hydraulic retention time of 10 h and was fed with methanol as the sole electron donor. The results show that the adaptation of the thermophilic, sulfidogenic methanol-degrading biomass to a high osmolarity environment is unlikely to occur. Sulfide was the main mineralization product from methanol degradation, regardless of the NaCl concentration added to the influent. However, sulfide production in the reactor steadily decreased after the addition of 7.5 g NaCl l(-1), whereas acetate production was stimulated at that influent NaCl concentration. Batch tests performed with sludge harvested from the UASB reactor when operating at different influent salinities confirmed that acetate is the main metabolic product at NaCl concentrations higher than 12.5 g l(-1). The apparent order of NaCl toxicity towards the different trophic groups was found to be: sulfate-reducing bacteria > methane-producing archaea > acetogenic bacteria.

Effect of NaCl on thermophilic (55 degrees C) methanol degradation in sulfate reducing granular sludge reactors.

The effect of NaCl on thermophilic (55 degrees C) methanol conversion in the presence of excess of sulfate (COD/SO(4)(2-)=0.5) was investigated in two 6.5L lab-scale upflow anaerobic sludge bed reactors inoculated with granular sludge previously not adapted to NaCl. Methanol was almost completely used for sulfate reduction in the absence of NaCl when operating at an organic loading rate of 5 g CODL(-1)day(-1) and a hydraulic retention time of 10h. The almost fully sulfidogenic sludge consisted of both granules and flocs developed after approximately 100 days in both reactors. Sulfate reducing bacteria (SRB) outcompeted methane producing archaea (MPA) for methanol, but acetate represented a side-product, accounting for maximal 25% of the total COD converted. Either MPA or SRB did not use acetate as substrate in activity tests. High NaCl concentrations (25 gL(-1)) completely inhibited methanol degradation, whereas low salt concentrations (2.5 g NaClL(-1)) provoked considerable changes in the metabolic fate of methanol. The MPA were most sensitive towards the NaCl shock (25 gL(-1)). In contrast, the addition of 2.5 gL(-1) of NaCl stimulated MPA and homoacetogenic bacteria.

Effect of high salinity on the fate of methanol during the start-up of thermophilic (55 degrees C) sulfate reducing reactors.

Two 6.5 L lab-scale upflow anaerobic sludge bed (UASB) reactors were operated at 55 degrees C fed with methanol as the sole electron and carbon source and in excess of sulfate (COD/SO4(2-) of 0.5) in order to investigate the effect of high wastewater salinity on the start-up period. The first reactor (UASB I) was operated without NaCl addition, while the second reactor (UASB II) was fed with 25 g x L(-1) of NaCl in the first 13 days of operation. Successful start-up of UASB I was achieved, with full methanol conversion (100% elimination) to methane gas (methane production rate up to 3.66 gCOD.L(-1).day(-1)). Despite the detection of sulfide from day 15 onwards in UASB I, methane was the main mineralization product when operating at an organic loading rate (OLR) of 5 gCOD.L(-1).day(-1) and a hydraulic retention time (HRT) of 10 hours. Sulfide and acetate started to be produced after salt omission from the influent in UASB II at day 13, with no detection of methane. Acetate was the main product when operating at an OLR of 10 gCOD.L(-1).day(-1) and HRT of 6.5 hours in both reactors. Apparently, the methane producing bacteria (MPB) are the trophic group most sensible to the NaCl shock.