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
Abstract: The economic factor of the microalgae harvesting step acts as a barrier to scaling up microalgae-based technology designed for wastewater treatment. In view of that, this study presents an alternative microalgae-bacteria system, which is proposed for eliminating the economic obstacle. Instead of the microalgae-bacteria (activated algae) flocs, the study aimed to develop activated algae granules comprising the microalgae Chlorella sp. as a target species. The presence of the filamentous microalgae (Phormidium sp.) was necessary for the occurrence of the granulation processes. A progressive decrease in frequency of the free Chlorella sp. cells was achieved once with the development of the activated algae granules as a result of the target microalgae being captured in the dense and tangled network of filaments. The mature activated algae granules ranged between 600 and 2,000 µm, and were characterized by a compact structure and significant settling ability (21.6 ± 0.9 m/h). In relation to the main aim of this study, a microalgae recovery efficiency of higher than 99% was achieved only by fast sedimentation of the granules; this performance highlighted the viability of the granular activated algae system for sustaining a microalgae harvesting procedure with neither cost nor energy inputs.
Pub.: 07 Jul '17, Pinned: 19 Aug '17
Abstract: The development and properties of algae-bacteria granular consortia, which cultivated with the algae (Chlorella and Scenedesmus) and aerobic granules, was investigated in this experiment. The results indicated that the granular consortia could be successfully developed by selection pressure control, and the algal biomass and extracellular polymeric substances (EPS) concentration in the consortia showed notable correlation with the operating parameters of reactor. The maximum specific removal rates of total nitrogen and phosphate were obtained from the granular consortia with the highest algal biomass, yet the correlation between the fatty acid methyl esters yield and the algal biomass in the consortia was not markedly observed. The seed algae maintained dominance in the phototroph community, whereas the cyanobacteria only occupied a small proportion (5.2-6.5%). Although the bacterial communities with different operational strategies showed significant difference, the dominated bacteria (Comamonadaceae, 18.79-36.25%) in the mature granular consortia were similar.
Pub.: 19 Feb '17, Pinned: 14 Aug '17
Abstract: The effect of algae growth on aerobic granulation and nutrients removal was studied in two identical sequencing batch reactors (SBRs). Sunlight exposure promoted the growth of algae in the SBR (Rs), forming an algal-bacterial symbiosis in aerobic granules. Compared to the control SBR (Rc), Rs had a slower granulation process with granules of loose structure and smaller particle size. Moreover, the specific oxygen uptake rate was significantly decreased for the granules from Rs with secretion of 25.7% and 22.5% less proteins and polysaccharides respectively in the extracellular polymeric substances. Although little impact was observed on chemical oxygen demand (COD) removal, algal-bacterial symbiosis deteriorated N and P removals, about 40.7-45.4% of total N and 44% of total P in Rs in contrast to 52.9-58.3% of TN and 90% of TP in Rc, respectively. In addition, the growth of algae altered the microbial community in Rs, especially unfavorable for Nitrospiraceae and Nitrosomonadaceae.
Pub.: 30 Dec '14, Pinned: 28 Jul '17
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
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
Abstract: Aerobic sludge granulation was rapidly obtained in the erlenmeyer bottle and sequencing batch reactor (SBR) using piggery wastewater. Aerobic granulation occurred on day 3 and granules with mean diameter of 0.2 mm and SVI30 of 20.3 mL/g formed in SBR on day 18. High concentrations of Ca and Fe in the raw piggery wastewater and operating mode accelerated aerobic granulation, even though the seed sludge was from a municipal wastewater treatment plant (WWTP). Alpha diversity analysis revealed Operational Taxonomic Units, Shannon, ACE and Chao 1 indexes in aerobic granules were 2013, 5.51, 4665.5 and 3734.5, which were obviously lower compared to seed sludge. The percentages of major microbial communities, such as Proteobacteria, Bacteroidetes and Firmicutes were obviously higher in aerobic granules than seed sludge. Chloroflexi, Planctomycetes, Actinobacteria, TM7 and Acidobacteria showed much higher abundances in the inoculum. The main reasons might be the characteristics of raw piggery wastewater and granule structure.
Pub.: 14 Jul '16, Pinned: 14 Aug '17
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
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
Abstract: This study investigated sludge granulation inoculated with various mixtures of aerobic and anaerobic sludge at low dissolved oxygen (DO; 0.3–0.6 mg/l) or aerobic (>2.5 mg/l) conditions in four parallel flow reactor systems. Formation of high-density coupled granules was achieved in the reactor system inoculated with anaerobic and aerobic sludge seeds (1:1 mass ratio) at low DO concentrations, with a mean size of 2.5 mm after only 27 days of cultivation. The highest ratio of protein (PN) to polysaccharide (PS; 3.3) was observed for the coupled sludge compared to granules cultivated under aerobic conditions. The PN/PS ratio correlated well with high hydrophobicity, low sludge volumetric index, and compact granular structure. Activity tests of the specific anaerobic and aerobic biomass confirmed that anaerobes and aerobes coexisted in the same coupled granule. Based on the optical microscopic and SEM observations, the process of coupled granule formation was proposed.
Pub.: 30 Sep '09, Pinned: 14 Aug '17
Abstract: Simultaneous nitrate (N), phosphate (P), and COD removal was investigated in photobioreactors containing both algae and bacteria. The reactors were operated in the semi-batch mode with a hydraulic retention time of 2 days. Reactors were operated in two phases, (1) with 33 % biomass recycle and (2) with no biomass recycle. In both phases, more than 90 % of N and P and 80 % of COD present in synthetic wastewaters with initial N and P concentrations of up to 110 and 25 mg/L, respectively, and initial COD of 45 mg/L could be removed. Biomass growth in reactors did not increase with the increase in initial N and P concentration in either phase. However, biomass growth was slightly more in reactors operated with no biomass recycle. In both phases, N and P uptake was greater in reactors with greater initial N and P concentrations. Also in all cases, N and P uptake in the reactors was far in excess of the stoichiometric requirements for the observed biomass growth. This "luxury uptake" of nitrogen and phosphorus by biomass was responsible for excellent nitrogen and phosphorus removal as observed. However, based on the results of this study, no advantage of biomass recycling could be demonstrated.
Pub.: 09 Oct '14, Pinned: 14 Aug '17
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
Abstract: An algal-bacterial culture, composed of wastewater-born algae and activated sludge, was cultivated to treat domestic wastewater and accumulate biomass simultaneously. The influence of algae and sludge inoculation ratios on the treatment efficiency and the settleability of the accumulated biomass were investigated. There was no significant effect of the inoculation ratios on the chemical oxygen demand removal. Comparatively, the nutrients removal and related mechanism were varied with different inoculation ratios. The highest nitrogen and phosphorus removal efficiencies were observed with 5:1 (algae/sludge) culture (91.0±7.0% and 93.5±2.5%, respectively) within 10 days, which was 5-40% higher and 2-4 days faster than those with other inoculation ratios. The biomass settleability was improved with the assistance of sludge, and the 1:5 (algae/sludge) culture showed the best settleability. Furthermore, 16S rDNA gene analysis showed that the bacterial communities were varying with different algae and sludge inoculation ratios and some specific bacteria were enriched during operation.
Pub.: 23 Dec '11, Pinned: 28 Jul '17