Low Retention Time Research Articles

New insights into impacts of anthropogenic nutrients on urban ecosystem processes on the Southern California coastal shelf: Introduction and synthesis

Anthropogenic nutrient inputs are one of the most important factors contributing to eutrophication of coastal waters. Coastal upwelling regions are naturally highly variable, exhibiting faster flushing and lower retention times than estuarine systems. As such, these regions are considered more resilient to anthropogenic influences than other coastal waters. Recent studies have shown our perception of the sustainability of these systems may be flawed and that anthropogenic nutrients can have an impact at local and regional spatial scales within these larger upwelling ecosystems. Maintenance of an outfall pipe discharging wastewater effluent to the Southern California Bight (SCB) provided an opportunity to study effects of anthropogenic nutrient inputs on a near-shore coastal ecosystem. The diversion of wastewater effluent from a primary, offshore outfall to a secondary, near-shore outfall set up a large-scale, in situ experiment allowing researchers to track the fate of wastewater plumes as they were “turned off” in one area and “turned on” in another. In this introduction to a special issue, we synthesize results of one such wastewater diversion conducted by the Orange County Sanitation District (OCSD) during fall 2012. Anthropogenic nitrogen (N) from point-source discharges altered biogeochemical cycling and the community composition of bacteria and phytoplankton. Nitrification of ammonium to nitrate in wastewater effluent close to outfalls constituted a significant source of N utilized by the biological community that should be considered in quantifying “new” production. The microbial-loop component of the plankton community played a significant role, exemplified by a large response of heterotrophic bacteria to wastewater effluent that resulted in nutrient immobilization within the bacterial food web. This response, combined with the photosynthetic inhibition of phytoplankton due to disinfection byproducts, suppressed phytoplankton responses. Our findings have ramifications for future studies and regulatory monitoring, emphasizing the need to consider chemical and biological responses to wastewater effluent in assessing effects of anthropogenic nutrient inputs on urbanized coastal ecosystems.

Microsieving in primary treatment: effect of chemical dosing.

Primary and chemically enhanced primary wastewater treatment with microsieving (disc or drum filtration) was studied at the large pilot scale at seven municipal wastewater treatment plants in Europe. Without chemical dosing, the reduction of suspended solids (SS) was (on average) 50% (20-65%). By introducing chemically enhanced primary treatment and dosing with cationic polymer only, SS removal could be controlled and increased to >80%. A maximum SS removal of >90% was achieved with a chemical dosing of >0.007 mg polymer/mg influent SS and 20 mg Al(3+)/L or 30 mg Fe(3+)/L. When comparing sieve pore sizes of 30-40 μm with 100 μm, the effluent SS was comparable, indicating that the larger sieve pore size could be used due to the higher loading capacity for the solids. Phosphorus removal was adjusted with the coagulant dose, and a removal of 95-97% was achieved. Moreover, microsieving offers favourable conditions for automated dosing control due to the low retention time in the filter.

Morphometry and retention time as forcing functions to establishment and maintenance of aquatic macrophytes in a tropical reservoir.

Macrophytes may constitute an important resource for several chemical, physical and biological processes within aquatic ecosystems. This study considers that in tropical reservoirs with low retention time and with low values of shoreline development (DL), the expansion and persistence of aquatic macrophytes are mainly reported to local conditions (e.g., hydrodynamic and wind exposure) rather than trophic status and depth of the euphotic zone. In this context, this study aimed at describing and comparing the incidence of aquatic macrophytes in a throughflowing, non-dendritic tropical reservoir. During February 2006 to November 2007, eight limnological surveys were performed quarterly within the Ourinhos Reservoir, and in the mouth areas of its tributaries. At the six sampling stations 30 variables were measured. The number of sites with plants varied between 21 and 38 and at the end of the 1st year the total richness was found. The sampling survey outcome the recognition of 18 species of aquatic macrophytes; Cyperaceae (2 genera and 1 species), Pontederiaceae (3 species) and Onarograceae (3 genera) were the families with higher diversity. Seven species (Typha domingensis Pers., Myriophyllum aquaticum (Vell.) Verdec, Salvinia auriculata Aubl., Eichhornia azurea (Sw.) Kunth, Eleocharis sp1, Eichhornia crassipes (Mart.) Solms, Oxycaryum cubense (Poepp. & Kunth) Lye) always were present and were more frequent in the sites. The occurrence of emergent species predominated (45.9%), followed by submersed rooted (24.5%), free floating (19.5%), floating rooted (9.7%) and free submersed (0.3%). Although limnological variables and the distribution of macrophytes have discriminated the same sampling points, the stepwise multiple linear regressions did not pointed out strong correspondences (or coherence) among the most constant and distributed macrophyte species and the selected limnological variables, as well the trophic statuses. Seeing the low relationship among limnological variables and macrophytes distribution, in the case of Ourinhos Reservoir, the results pointed out that the water turbulence, low DL and wind exposure are the main driving forces that determine its aquatic plant distribution, life forms and species composition.

A new method of two-phase anaerobic digestion for fruit and vegetable waste treatment

A novel method of two-phase anaerobic digestion where the acid reactor is operated at low pH 4.0 was proposed and investigated. A completely stirred tank acid reactor and an up-flow anaerobic sludge bed methane reactor were operated to examine the possibility of efficient degradation of lactate and to identify their optimal operating conditions. Lactate with an average concentration of 14.8g/L was the dominant fermentative product and Lactobacillus was the predominant microorganism in the acid reactor. The effluent from the acid reactor was efficiently degraded in the methane reactor and the average methane yield was 261.4ml/gCOD removed. Organisms of Methanosaeta were the predominant methanogen in granular sludge of methane reactor, however, after acclimation hydrogenotrophic methanogens enriched, which benefited for the conversion of lactate to acetate. The two-phase AD system exhibited a low hydraulic retention time of 3.56days and high methane yield of 348.5ml/g VS removed.

The potential of phosphate removal from dairy wastewater and municipal wastewater effluents using a lanthanum-modified bentonite

Adsorption is gaining interest as an effective advanced method for treatment of wastewater effluents with a high phosphorus concentration. The present work investigated the use of a bentonite–lanthanum clay (Phoslock®) which effectively reduced the amount of dissolved phosphate. Batch experiments were carried out in order to obtain adsorption equilibrium isotherms and kinetics with phosphate-spiked synthetic solutions. Different doses of Phoslock® clay were examined for their efficiency in removing phosphate from dairy wastewater and from two types of domestic wastewater treatment plant effluents (a sequenced batch reactor (SBR) and an activated sludge plant). The average maximum adsorption capacity ratio was 69mg Phoslock® per 1mg of phosphate removed from the phosphate-spiked synthetic solution. Nevertheless, a ratio of 100, 300 and 400mg Phoslock® per 1mg of phosphate was found for complete phosphate removal from the effluents of the dairy, the SBR and the activated sludge plant, respectively. The higher ratios are probably due to the presence of dissolved organic matter in the wastewater. Phosphate removal from the effluents was more efficient and faster with the increase in Phoslock® doses (up to 100% removal in the first 15min for the dairy wastewater). This study shows that bentonite–lanthanum clay can be used to design an adsorption treatment process for phosphate removal from water and wastewater with a low hydraulic retention time and minimal infrastructure.

SIFT-MS analysis of the removal of dimethyl sulphide, n-hexane and toluene from waste air by a two phase partitioning bioreactor

Dimethyl sulphide (DMS), n-hexane and toluene removal from a waste air was carried out by a two phase partitioning bioreactor (TPPR) containing a 25/75vol/vol silicone oil/water emulsion inoculated with activated sludge under continuous feeding conditions. The performance of the reactor was determined using two different measuring techniques, GC-FID and SIFT-MS in order to determine the feasibility of the SIFT-MS as analytical technique. The linearity between both measurement techniques indicated that SIFT-MS can be used as a suitable alternative to determine the bioreactor performance. When feeding the TPPR only with hexane, elimination capacities (EC) of 139, 164 and 242gm−3h−1 are reached for an inlet load (IL) of 350gm−3h−1 at respectively 30, 60 and 120s empty bed residence time (EBRT). If a mixture of DMS, hexane and toluene is fed to the bioreactor at an EBRT of 60s EC of respectively 45, 45 and 75gm−3h−1 are reached for the different compound at an IL of 100gm−3h−1. This indicates that a TPPR can be applied to treat a mixture of hydrophobic and hydrophilic compounds. Excessive growth of biomass in a TPPR can lead to deteriorated aeration and a decrease in performance. By using pulse injections, the net retention time of the compounds could be determined online, which is related to the aeration and air distribution within the reactor. A low net retention time indicates bad aeration and air distribution, resulting in a low reactor performance. Therefore the net retention time can be used as a parameter indicating when biomass needs to be purged or when the aqueous medium needs to be refreshed.

Influence of hydraulic retention time on indigenous microalgae and activated sludge process

Integration of the microalgae and activated sludge (MAAS) process in municipal wastewater treatment and biogas production from recovered MAAS was investigated by studying the hydraulic retention time (HRT) of semi-continuous photo-bioreactors. An average total nitrogen (TN) removal efficiency (RE) of maximum 81.5 ± 5.1 and 64.6 ± 16.2% was achieved at 6 and 4 days HRT. RE of total phosphorous (TP) increased slightly at 6 days (80 ± 12%) HRT and stabilized at 4 days (56 ± 5%) and 2 days (55.5 ± 5.5%) HRT due to the fluctuations in COD and N/P mass ratio of the periodic wastewater. COD and organic carbon were removed efficiently and a rapidly settleable MAAS with a sludge volume index (SVI_10) of less than 117 mL g−1 was observed at all HRTs. The anaerobic digestion of the untreated MAAS showed a higher biogas yield of 349 ± 10 mL g VS−1 with 2 days HRT due to a low solids retention time (SRT). Thermal pretreatment of the MAAS (120 °C, 120 min) did not show any improvement with biogas production at 6 days (269 ± 3 (untreated) and 266 ± 16 (treated) mL gVS−1), 4 days (258 ± 11(untreated) and 263 ± 10 (treated) mL gVS−1) and 2 days (308 ± 19 mL (treated) gVS−1) HRT. Hence, the biogas potential tests showed that the untreated MAAS was a feasible substrate for biogas production. Results from this proof of concept support the application of MAAS in wastewater treatment for Swedish conditions to reduce aeration, precipitation chemicals and CO2 emissions.

Bioavailability studies of curcumin–sophorolipid nano-conjugates in the aqueous phase: role in the synthesis of uniform gold nanoparticles

The major limiting factors for curcumin to be accepted as a modern drug, despite its widespread applications, are its low aqueous solubility, low retention time and poor bioavailability.

A case study of coupling upflow anaerobic sludge blanket (UASB) and ANITA™ Mox process to treat high-strength landfill leachate.

A pilot study was conducted to study the treatability of high-strength landfill leachate by a combined process including upflow anaerobic sludge blanket (UASB), carbon removal (C-stage) moving bed biofilm reactor (MBBR) and ANITA™ Mox process. The major innovation on this pilot study is the patent-pending process invented by Veolia that integrates the above three unit processes with an effluent recycle stream, which not only maintains the low hydraulic retention time to enhance the treatment performance but also reduces inhibiting effect from chemicals present in the high-strength leachate. This pilot study has demonstrated that the combined process was capable of treating high-strength leachate with efficient chemical oxygen demand (COD) and nitrogen removals. The COD removal efficiency by the UASB was 93% (from 45,000 to 3,000 mg/L) at a loading rate of 10 kg/(m(3)·d). The C-stage MBBR removed an additional 500 to 1,000 mg/L of COD at a surface removal rate (SRR) of 5 g/(m(2)·d) and precipitated 400 mg/L of calcium. The total inorganic nitrogen removal efficiency by the ANITA Mox reactor was about 70% at SRR of 1.0 g/(m(2)·d).

Variations in phosphorus retention by a solid material while scaling up its application

Abstract Significant reductions in phosphorus (P) inputs from point sources into bodies of water have been achieved in many countries, but curbing losses from non-point P sources still poses a challenge. One potential solution is to use solid P-retaining filters. In this study, we scaled up the application of a promising material (Sachtofer PR ® ) and observed the effects of variable flows, influent P concentrations, the presence of organic matter, and material alteration on P retention. The test set-ups included 1) a 6-g filter that received influents with a dissolved P concentration of 50 mg/l, 2) a 20-kg filter that received variable flow rates of tap and river water containing dissolved P amounts of up to 6 mg/l, and 3) a seven-ton filter constructed in a ditch that collected water (P concentration of up to 0.25 mg /l) from 17-ha of cropland. All filters achieved similar initial discrete P removals, but increasing the scale finally reduced cumulative P retention. The laboratory filter retained 19 mg P/g vs. 3.2 mg P/g for the meso-scale filter vs. 0.06 mg P/g for the large-scale filter, a result due largely to the decrease in the influent P concentration and the presence of humic substances. In addition, low retention times due to preferential flows and high-flow conditions greatly compromised the efficiency of the large filter. Filters should target critical sources and, consequently, the loading with significant amounts of P would improve their economic value while facilitating the future recovery and reuse of P.

Architecting the Last-Level Cache for GPUs using STT-RAM Technology

Future GPUs should have larger L2 caches based on the current trends in VLSI technology and GPU architectures toward increase of processing core count. Larger L2 caches inevitably have proportionally larger power consumption. In this article, having investigated the behavior of GPGPU applications, we present an efficient L2 cache architecture for GPUs based on STT-RAM technology. Due to its high-density and low-power characteristics, STT-RAM technology can be utilized in GPUs where numerous cores leave a limited area for on-chip memory banks. They have, however, two important issues, high energy and latency of write operations, that have to be addressed. Low retention time STT-RAMs can reduce the energy and delay of write operations. Nevertheless, employing STT-RAMs with low retention time in GPUs requires a thorough study on the behavior of GPGPU applications. Based on this investigation, we have architectured a two-part STT-RAM-based L2 cache with low-retention (LR) and high-retention (HR) parts. The proposed two-part L2 cache exploits a dynamic threshold regulator (DTR) to efficiently regulate the write threshold for migration of the data blocks from HR to LR, based on the behavior of the applications. Also, a Data and Access type Aware Cache Search mechanism (DAACS) is hired for handling the search of the requested data blocks in two parts of the cache. The STT-RAM L2 cache architecture proposed in this article can improve IPC by up to 171% (20% on average), and reduce the average consumed power by 28.9% compared to a conventional L2 cache architecture with equal on-chip area.

A UASB reactor coupled to a hybrid aerobic MBR as innovative plant configuration to enhance the removal of organic micropollutants

An innovative plant configuration based in an UASB reactor coupled to a hybrid aerobic membrane bioreactor designed for sustainable treatment of municipal wastewater at ambient temperatures and low hydraulic retention time was studied in terms of organic micropollutants (OMPs) removal. OMPs removal mechanisms, as well as the potential influence of biomass activity and physical conformation were assessed. Throughout all periods of operation (150 days) high organic matter removals were maintained (>95%) and, regarding OMPs removal, this innovative system has shown to be more efficient than conventional technologies for those OMPs which are prone to be biotransformed under anaerobic conditions. For instance, sulfamethoxazole and trimethoprim have both shown to be biodegradable under anaerobic conditions with similar efficiencies (removal efficiencies above 84%). OMPs main removal mechanism was found to be biotransformation, except in the case of musk fragrances which showed medium sorption onto sludge. OMPs removal was strongly dependent on the efficiency of the primary metabolism (organic matter degradation and nitrification) and the type of biomass.

Anaerobic dynamic membrane bioreactor for wastewater treatment at ambient temperature

A bench-scale dynamic membrane (DM) bioreactor was operated to evaluate the anaerobic treatment of a synthetic municipal wastewater at ambient temperature. The DM was developed over a large pore size (200μm) mesh in order to improve sludge filterability and reduce energy consumption. The system achieved average organic removals higher than 80% and 90% for total COD and filtered COD, respectively. Results also demonstrated that the biofilm, which the DM is made of, played a significant part in obtaining the overall organic removal efficiency. The large pore size of the mesh allowed for high membrane fluxes (approximately 15–20Lm−2h−1) applying low TMP (usually lower than 50–100mbar). Fluxes higher than 20Lm−2h−1 produced low solid removal efficiency indicating deterioration of the DM. COD mass balance suggests that the low hydraulic retention times applied to the system caused methane loss through the effluent due to oversaturation.

Photosynthetic aeration in biological wastewater treatment using immobilized microalgae-bacteria symbiosis.

Chlorella vulgaris encapsulated in alginate beads were added into a bioreactor treating synthetic wastewater using Pseudomonas putida. A symbiotic CO2/O2 gas exchange was established between the two microorganisms for photosynthetic aeration of wastewater. During batch operation, glucose removal efficiency in the bioreactor improved from 50% in 12 h without aeration to 100% in 6 h, when the bioreactor was aerated photosynthetically. During continuous operation, the bioreactor was operated at a low hydraulic retention time of 3.3 h at feed concentrations of 250 and 500 mg/L glucose. The removal efficiency at 500 mg/L increased from 73% without aeration to 100% in the presence of immobilized microalgae. The initial microalgae concentration was critical to achieve adequate aeration, and the removal rate increased with increasing microalgae concentration. The highest removal rate of 142 mg/L-h glucose was achieved at an initial microalgae concentration of 190 mg/L. Quantification of microalgae growth in the alginate beads indicated an exponential growth during symbiosis, indicating that the bioreactor performance was limited by oxygen production rates. Under symbiotic conditions, the chlorophyll content of the immobilized microalgae increased by more than 30%. These results indicate that immobilized microalgae in symbiosis with heterotrophic bacteria are promising in wastewater aeration.

Performance of sulphate- and selenium-reducing biochemical reactors using different ratios of labile to recalcitrant organic materials.

Successful operation of sulphate-reducing bioreactors using complex organic materials depends on providing a balance between more easily degrading material that achieves reasonable kinetics and low hydraulic retention times, and more slowly decomposing material that sustains performance in the long term. In this study, two organic mixtures containing the same ingredients typical of bioreactors used at mine sites (woodchips, hay and cow manure) but with different ratios of wood (recalcitrant) to hay (labile) were tested in six continuous flow bioreactors treating synthetic mine-affected water containing 600 mg/L of sulphate and 15 μg/L of selenium. The reactors were operated for short (5-6 months) and long (435-450 days) periods of time at the same hydraulic retention time of 15 days. There were no differences in the performance of the bioreactors in terms of sulphate-reduction over the short term, but the wood-rich bioreactors experienced variable and sometimes unreliable sulphate-reduction over the long term. Presence of more hay in the organic mixture was able to better sustain reliable performance. Production of dissolved organic compounds due to biodegradation within the bioreactors was detected for the first 175-230 days, after which their depletion coincided with a crash phase observed in the wood-rich bioreactors only.

Improved yield and higher heating value of biochar from oil palm biomass at low retention time under self-sustained carbonization

Oil palm biochar with high yield and higher heating value under low energy requirement is required for improved waste management and utilization in the palm oil industry. This paper presents, a self-sustained carbonization of oil palm empty fruit bunch biomass, without internal heating element, which produced high biochar yield and higher heating value. Three different particle sizes of pressed-shredded oil palm empty fruit bunch biomass, i.e. below 29 mm, 30–99 mm and 100–150 mm, at 8–10% moisture content were used. The carbonization temperature was monitored and used as an indicator to stop the carbonization prior to harvesting. The maximum carbonization temperature recorded was 600 °C. In our previous report, harvested at 300 °C under uncontrolled exhausted air flow rate and found that the higher heating values obtained were 23.0–25.0 MJ/kg. However the biochar yield was only 14–16 %. In order to increase the yield of biochar, the exhaust air flow rate has been fixed at 36 m3/hr by using an air suction blower to ensure uniform circulation and distribution of hot air from top to bottom before being discharged. The biochar was harvested when the temperature of the bed decreased to 500 °C. The particle size range from 100 to 150 mm produced the highest biochar yield of 26.0 ± 1.2% with higher heating value of 23.0–23.5 MJ/kg within 5–8 h retention time. The gaseous emissions were lower than permitted level set by the environmental authorities. The technology developed in this study should be used to improve the management and utilization of oil palm biomass towards a more sustainable palm oil industry.

Performance and enhanced mechanism of a novel bio-diatomite biofilm pretreatment process treating polluted raw water

A lab-scale novel bio-diatomite biofilm process (BDBP) was established for the polluted raw water pretreatment in this study. Results showed that a shorter startup period of BDBP system was achieved under the completely circulated operation mode, and the removal efficiencies of nitrogen and disinfection by-product precursor were effective at low hydraulic retention time of 2–4h due to high biomass attached to the carrier and diatomite. A maximum NH4+-N oxidation potential predicted by modified Stover–Kincannon model was 333.3mgL−1d−1 in the BDBP system, which was 4.7 times of that in the control reactor. Results demonstrated that the present of bio-diatomite favors the accumulation of functional microbes in the oligotrophic niche, and the pollutants removal performance of this novel process was enhanced for polluted raw water pretreatment.

Co-digestion of municipal sludge and external organic wastes for enhanced biogas production under realistic plant constraints

A bench-scale investigation was conducted to select external organic wastes and mixing ratios for co-digestion with municipal sludge at the F. Wayne Hill Water Resources Center (FWHWRC), Gwinnett County, GA, USA to support a combined heat and power (CHP) project. External wastes were chosen and used subject to two constraints: a) digester retention time no lower than 15 d; and b) total biogas (methane) production not to exceed a specific target level based on air permit constraints on CO2 emissions. Primary sludge (PS), thickened waste activated sludge (TWAS) and digested sludge collected at the FWHWRC, industrial liquid waste obtained from a chewing gum manufacturing plant (GW) and dewatered fat-oil-grease (FOG) were used. All sludge and waste samples were characterized and their ultimate digestibility was assessed at 35 °C. The ultimate COD to methane conversion of PS, TWAS, municipal sludge (PS + TWAS; 40:60 w/w TS basis), GW and FOG was 49.2, 35.2, 40.3, 72.7, and 81.1%, respectively. Co-digestion of municipal sludge with GW, FOG or both, was evaluated using four bench-scale, mesophilic (35 °C) digesters. Biogas production increased significantly and additional degradation of the municipal sludge between 1.1 and 30.7% was observed. Biogas and methane production was very close to the target levels necessary to close the energy deficit at the FWHWRC. Co-digestion resulted in an effluent quality similar to that of the control digester fed only with the municipal sludge, indicating that co-digestion had no adverse effects. Study results prove that high methane production is achievable with the addition of concentrated external organic wastes to municipal digesters, at acceptable higher digester organic loadings and lower retention times, allowing the effective implementation of CHP programs at municipal wastewater treatment plants, with significant cost savings.

A bloom of cyanobacteria (Cylindrospermopsis raciborskii) in UHE Carlos Botelho (Lobo/Broa) reservoir: a consequence of global change?

; periodic turbulence with re-oxygenation of the whole water column, and high saturation of oxygen (80-100%); low retention time (< 20 days) and a extensive macrophyte grow in the headwaters that prevent high nutrient load. This is the picture for the last 44 years. The phytoplankton composition was consistent with the oligomesotrophic characteristic of the reservoir: predominance of diatoms and chlorophyceae with a maximum of 10µg/l chlorophyll. However in the winter of (july) 2014 the following changes were observed: a heavy bloom of cyanobacteria occurred for the first time in the reservoir. This cyanobacteria Cylindrospermopsis raciborskii, is a invasive species. Very high chlorophyll levels (up to 100µg/l) were measured and high concentration and input of phosphorus was also detected (Tundisi and Matsumura-Tundisi, 2014). The explanation for this sudden appearance of blooms, can be attributed to the following factors: increase of up to 2°C above the average water temperature during the winter; lower rainfall during summer (30% less of the yearly average of 1.500 mm). Increase in the retention time (from <20 days up to 60 days) in order to maintain volumes for hydroelectricity production. This cyanobacteria bloom can be attributed to changes in the regional climate and the hydrological regime, with consequences for the dam operation. As described by Paerl and Huisman (2008), global warming affects patterns of precipitation and drought. The changes in the hydrological cycle enhanced cyanobacterial dominance. Heavy rains after extensive drought periods, increase nutrient input promoting phytoplankton growth. During periods of drought ,residence time, increase, thus promoting blooms.

Integration of the Anammox process to the rejection water and main stream lines of WWTPs

Nowadays the application of Anammox based processes in the wastewater treatment plants has given a step forward. The new goal consists of removing the nitrogen present in the main stream of the WWTPs to improve their energetic efficiencies. This new approach aims to remove not only the nitrogen but also to provide a better use of the energy contained in the organic matter. The organic matter will be removed either by an anaerobic psychrophilic membrane reactor or an aerobic stage operated at low solids retention time followed by an anaerobic digestion of the generated sludge. Then ammonia coming from these units will be removed in an Anammox based process in a single unit system. The second strategy provides the best results in terms of operational costs and would allow reductions of about 28%.Recent research works performed on Anammox based processes and operated at relatively low temperatures and/or low ammonia concentrations were carried out in single-stage systems using biofilms, granules or a mixture of flocculent nitrifying and granular Anammox biomasses. These systems allowed the appropriated retention of Anammox and ammonia oxidizing bacteria but also the proliferation of nitrite oxidizing bacteria which seems to be the main drawback to achieve the required effluent quality for disposal. Therefore, prior to the implementation of the Anammox based processes at full scale to the water line, a reliable strategy to avoid nitrite oxidation should be defined in order to maintain the process stability and to obtain the desired effluent quality. If not, the application of a post-denitrification step should be necessary.