New concepts on carbon redirection in wastewater treatment plants: A review.

Wastewater treatment plants (WWTPs) are no longer considered pollution removal systems but rather resources (nutrients and energy) recovery plants. Legislation imposing more stringent effluent requirements and the need energy self-sufficient or even energy-positive plants are the main drivers for the research and development of new WWTP configurations. While a lot of effort has been focused on developing new processes for nutrient recovery, limited efforts have been allocated to maximizing energy recovery from the organic load. Within this context, high-rate activated sludge (HRAS) is the most promising alternative technology to redirect carbon (organic compounds) towards energy as biogas. This is a critical review of the last decade's development of new alternatives for carbon redirection to improve the energy balance of WWTPs on both the laboratory and the industrial scale.

Recovery of ammonia from domestic wastewater effluents as liquid fertilizers by integration of natural zeolites and hollow fibre membrane contactors.

The integration of up-concentration processes to increase the efficiency of primary sedimentation, as a solution to achieve energy neutral wastewater treatment plants, requires further post-treatment due to the missing ammonium removal stage. This study evaluated the use of zeolites as a post-treatment step, an alternative to the biological removal process. A natural granular clinoptilolite zeolite was evaluated as a sorbent media to remove low levels (up to 100mg-N/L) of ammonium from treated wastewater using batch and fixed bed columns. After being activated to the Na-form (Z-Na), the granular zeolite shown an ammonium exchange capacity of 29±0.8mgN-NH4+/g in single ammonium solutions and 23±0.8mgN-NH4+/g in treated wastewater simulating up-concentration effluent at pH=8. The equilibrium removal data were well described by the Langmuir isotherm. The ammonium adsorption into zeolites is a very fast process when compared with polymeric materials (zeolite particle diffusion coefficient around 3×10-12m2/s). Column experiments with solutions containing 100mgN-NH4+/L provide effective sorption and elution rates with concentration factors between 20 and 30 in consecutive operation cycles. The loaded zeolite was regenerated using 2g NaOH/L solution and the rich ammonium/ammonia concentrates 2-3g/L in NaOH were used in a liquid-liquid membrane contactor system in a closed-loop configuration with nitric and phosphoric acid as stripping solutions. The ammonia recovery ratio exceeded 98%. Ammonia nitrate and di-ammonium phosphate concentrated solutions reached up to 2-5% wt. of N.

Comparison of aerobic granulation and anaerobic membrane bioreactor technologies for winery wastewater treatment.

An anaerobic membrane bioreactor and aerobic granulation technologies were tested at laboratory scale to treat winery wastewater, which is characterised by a high and variable biodegradable organic load. Both technologies have already been tested for alcohol fermentation wastewaters, but there is a lack of data relating to their application to winery wastewater treatment. The anaerobic membrane bioreactor, with an external microfiltration module, was started up for 230 days, achieving a biogas production of up to 0.35 L CH4L(-1)d(-1) when 1.5 kg COD m(-3)d(-1) was applied. Average flux was 10.5 L m(-2) h(-1) (LMH), obtaining a treated effluent free of suspended solids and a chemical oxygen demand (COD) concentration lower than 100 mg COD L(-1). In contrast, the aerobic granular sequencing batch reactor coped with 15 kg COD m(-3)d(-1), but effluent quality was slightly worse. Aerobic granulation was identified as a suitable technique to treat this kind of wastewater due to excellent settleability, high biomass retention and a good ability to handle high organic loads and seasonal fluctuations. However, energy generation from anaerobic digestion plays an important role, favouring anaerobic membrane bioreactor application, although it was observed to be sensitive to sudden load fluctuations, which led to a thorough pH control and alkali addition.

Partial nitrification of sludge reject water by means of aerobic granulation.

Granular sludge formation was performed in a laboratory scale Sequencing Batch Reactor (SBR) fed with supernatant of anaerobic digestion of sewage sludge. This effluent was concentrated progressively in order to enhance biomass capacity without inhibiting it. During the first part of the study, ammonium nitrogen was converted to nitrate, so conventional nitrification took place. When a nitrogen load of 0.8 g N L(-1) d(-1) was treated, the effluent concentration of nitrite started to increase while the nitrate concentration decreased until it disappeared. So, partial nitrification was achieved. At the end of this study, a nitrogen load of 1.1 g N L(-1) d(-1) was treated obtaining an effluent with 50% ammonium and 50% nitrite. The volatile suspended solids concentration in the reactor reached 10 g VSS L(-1). At this point the granule morphology was quite round and no filamentous bacteria was observed. The Feret's diameter was in the range between 1 and 6 mm with an average value of 4.5 mm. Roundness value was all the time higher than 0.7. Granule density increased during the experimental period, obtaining a final value of 7.0 g L(-1).

Start-up of an aerobic granular sequencing batch reactor for the treatment of winery wastewater.

Aerobic granular sludge was cultivated in a sequencing batch reactor (SBR) in order to remove the organic matter present in winery wastewater. The formation of granules was performed using a synthetic substrate. The selection parameter was the settling time, as well as the alternation of feast-famine periods, the air velocity and the height/diameter ratio of the reactor. After 10 days of operation under these conditions, the first aggregates could be observed. Filamentous bacteria were still present in the reactor but they disappeared progressively. During the start-up, COD loading was increased from 2.7 to 22.5 kg COD/(m(3) day) in order to obtain a feast period between 30 and 60 minutes. At this point, granules were quite round, with a particle diameter between 3.0 and 4.0 mm and an average density of 6 g L(-1). After 120 days of operation, synthetic media was replaced by real winery wastewater, with a COD loading of 6 kg COD/(m(3) day). The decrease of the organic load implied a reduction of the aggregate diameter and a density increase up to 13.2 g L(-1). The effluent was free of organic matter and the solids concentration in the reactor reached 6 g VSS L(-1).

SBR technology for high ammonium loading rates.

This paper focuses on the study of high ammonium concentrated wastewater with SBR reactors. Four type of wastewaters, landfill leachates (T=20 degrees C) and the reject water (T=35 degrees C) coming from mesophilic anaerobic digesters of sewage sludge, pig slurry and organic fraction of municipal solid waste (OFMSW), were studied in four SBR during 6 months. The removal of nitrogen was done in all the cases with nitrification/denitrification via nitrite obtaining high removal nitrogen conversions for the three types of reject water (0.75-0.85 kg N day(-1) m(-3)) and lower for landfill leachates due to temperature requirements (0.3 kg N day(-1) m(-3)).

Study of the biological N removal over nitrite in a physico-chemical-biological treatment of digested pig manure in a SBR.

SBR technology is used to treat the supernatant from mesophilic anaerobic digestion of piggery wastewater. The novelty of the treatment consists in the use of a final coagulation/flocculation step inside the SBR cycle to reach the legal COD effluent standard. The pH changes introduced by the use of FeCl(3) do not affect the nitrifying activity. The SBR treatment includes a strategy to the control of oxygen supply and ammonia concentrations inside the digester to favor the biological nitrogen removal over nitrite, which makes the process more economical. The influence of several of these parameters on the AOB biomass activity is studied in this paper.