A pinboard by
Ahmed Abouhend

I am a PhD student in Environmental and Water Resources Engineering Program at UMass Amherst, USA.


A new direction for wastewater treatment with huge energy savings

Wastewater treatment is an energy-intensive industry. About 2.16 MJ of energy is required for the treatment of 1 m3 of wastewater. Since 1912-1914, activated sludge process is the most common technology for wastewater treatment. In activated sludge system, mechanical aeration is required to provide oxygen to the biological flocs (bacteria). Then, the bacterial flocs use this oxygen to oxidize the organic matter and ammonia from wastewater. The process involves oxygen being introduced into the activated sludge system accounts for 25-60% of the overall operational costs. Besides, activated sludge does not settle very well so settling tanks are required to allow the biological flocs to settle. Using physical or chemical methods to enhance biomass separation from water is additional costs. Over the last two decades, granular sludge (growing the bacterial sludge as granules NOT flocs) has been widely used to enhance biomass settling and separation from water. Although granulation of activated sludge has operational benefits, it still requires high-energy expenses because of the need for aeration. On the other hand, untreated wastewater holds more than 10 times the energy used to treat it. If we can capture this potential energy from wastewater, the wastewater treatment process might become an energy producer rather than a consumer. We propose the oxygenic photogranule (OPG) process for aeration-free wastewater treatment. OPG process is a light-driven wastewater treatment that eliminates the need for mechanical aeration to treat wastewater. These photogranules are enriched with a phototrophic community (cyanobacteria, microalgae) that produces O2 needed for oxidizing organic matter and treating wastewater. Under sunlight, the phototrophs autonomously produce O2 through photosynthesis, which in the activated sludge process should be provided by energy-intensive aeration. In turn, the heterotrophic bacteria within the OPG uses this oxygen to oxidize the organic matter in wastewater and produces CO2 for phototrophs. We evaluated the feasibility of these granules for wastewater treatment in bench and pilot scales. The OPG process can cut the wastewater treatment costs in half through sustaining self-aeration process. Besides, the easily harvested phototrophic biomass could be converted through various pathways to biofuels. This phototrophic biogranule technique would allow wastewater treatment plants to generate most of the energy needed for plant operation


Formation of aerobic granules for the treatment of real and low-strength municipal wastewater using a sequencing batch reactor operated at constant volume.

Abstract: This study aimed at evaluating the formation of aerobic granular sludge (AGS) for the treatment of real and low-strength municipal wastewater using a column sequencing batch reactor (SBR) operated in fill-draw mode (constant volume). The focus was on understanding how the wastewater upflow velocity (VWW) applied during the anaerobic feeding influenced the sludge properties and in turn the substrate conversion. Two different strategies were tested: (1) washing-out the flocs by imposing high wastewater upflow velocities (between 5.9 and 16 m h(-1)) during the anaerobic feeding (Approach #1) and (2) selective utilization of organic carbon during the anaerobic feeding (1 m h(-1)) combined with a selective sludge withdrawal (Approach #2). A column SBR of 190 L was operated in constant volume during 1500 days and fed with real and low-strength municipal wastewater. The formation of AGS with SVI30 of around 80 mL gTSS(-1) was observed either at very low (1 m h(-1)) or at high VWW (16 m h(-1)). At 16 m h(-1) the AGS was mainly composed of large and round granules (d > 0.63 mm) with a fluffy surface, while at 1 m h(-1) the sludge was dominated by small granules (0.25 < d < 0.63 mm). The AGS contained a significant fraction of flocs during the whole operational period. A considerable and continuous washout of biomass occurred at VWW higher than 5.9 m h(-1) (Approach #1) due to the lower settling velocity of the AGS fed with municipal wastewater. The low sludge retention observed at VWW higher than 5.9 m h(-1) deteriorated the substrate conversion and in turn the effluent quality. High solid concentrations (and thus solid retention time) were maintained during Approach #2 (VWW of 1 m h(-1)), which resulted in an excellent effluent quality. The study demonstrated that the formation of AGS is possible during the treatment of real and low-strength municipal wastewater in a SBR operated at constant volume. Low wastewater upflow velocities should be applied during the anaerobic feeding phase in order to ensure enough biomass retention and efficient substrate removal.

Pub.: 19 Sep '16, Pinned: 14 Aug '17

Rapid Formation of Aerobic Granular Sludge and Its Mechanism in a Continuous-Flow Bioreactor.

Abstract: Based on the principle of self-coagulation of microorganisms, the flocculant-producing denitrifying bacterial TN-14 sludge was added to the continuous-flow reactor for treating domestic sewage. The bacterial TN-14 sludge acted as the main seed sludge to promote the rapid formation of aerobic granular sludge. The sludge morphology, sludge volume index (SVI) values, amounts of extracellular polymeric substances (EPS), and the role of calcium in the granulation process of the sludge were investigated. Results showed that brown aerobic granules with the particle size of 0.5 ~ 2.0 mm was successfully cultivated at 40 days, and its SVI30 decreased from 122.62 mL g(-1) initially to 46.61 mL g(-1) and remained at 44.28 ~ 60.51 mL g(-1) afterwards. The protein (PN) content in sludge EPS increased from 76.4 mg g(-1) initially to 512.3 mg g(-1). Compared with PN, the polysaccharide (PS) content did not change much throughout the operation process of the bioreactor. Energy-dispersive spectrum (EDS) showed that Ca elements were deposited inside the granular sludge, and X-ray diffraction (XRD) showed that Ca elements existed in the granular sludge in the forms of CaCO3, K2CaP2O7, Ca2P2O7, and Ca4O(PO4)2. The formation mechanism of continuous-flow aerobic granular sludge was that bacterial TN-14 sludge could promote the EPS content of sludge, and PN content of EPS increases the hydrophobicity and settling performance of the sludge. Calcium mainly exists in the granular sludge in the form of inorganic calcium phosphate, and therefore plays the role of nucleation in sludge granulation.

Pub.: 08 Sep '16, Pinned: 14 Aug '17

2,4-Dinitrotoluene removal in aerobic granular biomass sequencing batch reactors

Abstract: Aerobic granules were cultivated in sequencing batch reactor (SBR) by feeding 2,4-dinitrotoluene (2,4-DNT) along with acetate. Aerobic granules with an SVI10 of 34.57 ± 2.6 mL g−1 and average diameter of 0.78 ± 0.3 mm were formed during 30 d of SBR start-up period. In an alternative approach, aerobic granules cultivated using acetate as carbon source were acclimatized and evaluated for 2,4-DNT removal. In both the approaches, the aerobic granules exhibited rapid 2,4-DNT removal wherein >90% of 10 mg L−1 2,4-DNT was removed within 24 h cycle period. The aerobic granules also exhibited ammonium-nitrogen and phosphorus removal in addition to organic carbon removal, indicating that presence of 2,4-DNT did not negatively affect nutrient removal. In aerobic granular biomass reactors, most of the organic carbon was consumed within the first 6 h while, majority of the 2,4-DNT was removed during the 24 h cycle period. HPLC analysis detected smaller amounts of 2-amino-4-nitrotoluene, a biotransformation product of 2,4-DNT. 2,4-DNT removal by granules under anaerobic conditions was observed to be much smaller compared to the aerobic SBR. Thus, 2,4-DNT removal by aerobic granules was likely mediated by combination of both oxidative and reductive pathways. Although, the mechanisms of 2,4-DNT removal requires further investigations, effective and stable removal of 2,4-DNT in aerobic granular biomass reactors offers practical possibilities for treatment of wastewaters from ammunition factories.

Pub.: 07 Nov '16, Pinned: 14 Aug '17

The Development of Aerobic Granules from Conventional Activated Sludge under Anaerobic-Aerobic Cycles and Their Adaptation for Treatment of Dyeing Wastewater

Abstract: In the present study aerobic granules were formed from conventional activated sludge under anaerobic-aerobic cycles in synthetic media and subsequently used for treatment of real dyeing wastewater. Mature aerobic granules, characterised by their consumption of loosely bound extracellular polymeric substances (LB-EPS), and with%GR0.3 (percentage of granules with size ⩾ 0.3 mm) that exceeded 80%, were formed after 94 days of operation. Scanning electron microscope (SEM) structural analysis of the aerobic granules pointed to the possibility of the occurrence of azo dye decolorisation inside the aerobic granules during the aerobic phase of sequencing batch reactor (SBR) cycle. The presence of statistically meaningful correlations between total EPS, tightly bound EPS (TB-EPS) - including its protein (PN) and carbohydrate (PS) fraction and their ratio (PN/PS) - with%GR0.5 (percentage of granules with size ⩾ 0.5 mm) and SVI30 were identified, with the protein component of TB-EPS having the greatest influence. A hitherto unreported trend of change of EPS during both the anaerobic and aerobic phase and COD during the anaerobic phase was observed. The aerobic granules were successfully adapted to real dyeing wastewater with 73% color removal and 68% COD removal being achieved with a cycle time of 24 hours and ratio of anaerobic to aerobic period of 3. Measurement of anaerobic and aerobic color removal revealed aerobic dye decolorisation in the anaerobic core of the aerobic granules up to the point where the%GR0.3 was above 50%. However, during the 94 days adaptation period, despite the increase in both total EPS and PN/PS ratio in the greater part of SBR operation,%GR0.3 showed a continuous drop from 81% to 31%.

Pub.: 29 Nov '16, Pinned: 14 Aug '17

Municipal wastewater treatment and biomass accumulation with a wastewater-born and settleable algal-bacterial culture.

Abstract: A wastewater-born and settleable algal-bacterial culture, cultivated in a stirred tank photobioreactor under lab conditions, was used to remove the carbon and nutrients in municipal wastewater and accumulate biomass simultaneously. The algal-bacterial culture showed good settleable property and could totally settle down over 20 min, resulting in a reduction of total suspended solids from an initial 1.84 to 0.016 g/l. The average removal efficiencies of chemical oxygen demand, total kjeldahl nitrogen and phosphate were 98.2 ± 1.3%, 88.3 ± 1.6% and 64.8 ± 1.0% within 8 days, respectively, while the average biomass productivity was 10.9 ± 1.1 g/m(2) · d. Accumulation into biomass, identified as the main nitrogen and phosphorus removal mechanism, accounted for 44.9 ± 0.4% and 61.6 ± 0.5% of total inlet nitrogen and phosphorus, respectively. Microscopic analysis showed the main algae species in the bioreactor were filamentous blue-green algae. Furthermore, denaturing gradient gel electrophoresis and 16S rDNA gene sequencing revealed that the main bacteria present in the photobioreactor were consortia with sequences similar to those of Flavobacteria, Gammaproteobacteria, Bacteroidia and Betaproteobacteria. This study explores a better understanding of an algae-bacteria system and offers new information on further usage of biomass accumulated during treatment.

Pub.: 26 Apr '11, Pinned: 28 Jul '17