Low-strength Synthetic Wastewater Research Articles

Acceleration of the startup process of an anaerobic baffled reactor utilizing electrolyte regeneration

The objective of this study was to examine the performance of an electrolytic anaerobic baffled reactor (EABR) that contained five rectangular compartments in the treatment of low-strength synthetic wastewater. The effect of integration of electrolysis into an anaerobic baffled reactor (ABR) on the startup process, removal of chemical oxygen demand (COD), production of volatile fatty acids (VFAs), and profile of the pH of the EABR were investigated. With a low-strength influent (COD = 600 mg/L), the results indicated that COD removal was 92 % and that the VFAs were negligible by the third compartment. Also, VFA analysis showed that propionic acid was found in the first two compartments. This finding is aligned with compartment-wise profiles of COD removal, which was the highest in the initial compartments and which decreased longitudinally down the reactor. Monitoring the pH profile elucidated that the largest drop in pH was observed in the first two compartments, which is attributed to acidogenesis and acetogenesis activities. The proposed integration could decrease the startup process time to 12 d or less for low-strength feed of synthetic wastewater. This study demonstrated the significance of maintaining a stable pH for the optimal functioning of a diverse bacterial community by integrating bioelectrochemical processing in anaerobic digestion, as well as the application of the potential strategies to optimize the startup process of ABR. The optimization of the startup process of ABR through the integration of bioelectrochemical processing can contribute to Sustainable Development Goal 9 (Industry, Innovation, and Infrastructure) by promoting sustainable technological advancements and fostering sustainable industrialization.

Achieving partial nitrification by harnessing basic hydrolysis of sulphide salts amid high dissolved oxygen conditions

Attempts are going on to incorporate sulphur into the carbon and nitrogen removal processes at a biological wastewater treatment plant by external dosing or its intrinsic presence. A possible form of dosing sulphide at the field scale is the external dosing as the sodium salt of sulphide which under basic hydrolysis increases the pH. We demonstrated that the sodium salt dosage of sulphide can also be useful in achieving partial nitrification (PN). The results showed that 15 mgS/L of the sodium salt of sulphide was sufficient to establish PN in the low-strength synthetic and real wastewater under adequate dissolved oxygen concentrations (1.3 ± 0.4 mg/L during discharge phase of SBR cycle to 5.3 ± 0.2 mg/L during aeration phase of SBR cycle). PN was achieved only during the operational phases when the pH rise due to the basic hydrolysis of sodium sulphide was not controlled. The dosage of sulphide as its sodium salt has dual advantages as an inhibitor to nitrite oxidising bacteria (NOB). The activity of NOBs was 10–20 mgN/gVSS/d during the operational phases when PN was effective. The long-term operation showed a nitrite accumulation ratio of 70 ± 19% with an effluent ammonia concentration of 19 ± 4 mgN/L and nitrite concentrations of 18 ± 4 mgN/L. At the genus level, the NOB communities Nitrospira and Nitrobacter diminished in the long-term phases of stable PN with real wastewater. NOB communities evolved again when sulphide dosage was stopped indicating this strategy needs to be adopted continuously to achieve PN not time-based. The study demonstrated a strategy to achieve the feasibility of sulfide-driven PN systems and has a potential application in nitrogen removal from domestic wastewater.

A comparative study for hybrid UASB reactor performance using polyethylene media and luffa sponge as biofilm support.

This paper study the performance of a lab-scale hybrid up-flow anaerobic sludge blanket (UASB) reactor treating low-strength synthetic wastewater using different biofilm supporting materials. Two identical reactors are constructed and operated at constant up-flow velocity of 0.1m/hr., inflow rate of 9.76L/d, and hydraulic retention time (HRT) of 8.26hours. The Start-up phase, using seed sludge for existing wastewater treatment plant, lasted until the efficiency of chemical oxygen demand (COD) removal of both reactors reached 80%. Polyethylene (PE) media are added to one of the reactors and luffa sponge is used in the second reactor. Results show increased COD removal efficiency up to about 90% at 20°C and biogas production rates from 3.8*10-3 till 7.5*10-3m3 CH4/kg CODr using PE media. The COD removal efficiency reaches about 95% at 20°C using luffa sponge and biogas production rates up to 6.5*10 -3m3 CH4/kg CODr are achieved before clogging problem is observed. Effect of HRT reduction, from 8.26 to 4.13hours, on removing clogging is investigated. Reduction in COD removal efficiencies is observed at low ambient temperatures during seasonal variations of 15-25°C. AFM and SEM analysis are used to examine sludge granulation and biofilm formation.

Calcium-modified granular attapulgite removed phosphorus from synthetic wastewater containing low-strength phosphorus

Traditional biological processes combined with chemical precipitation methods can effectively reduce phosphate concentration in wastewater. However, discharge standards required additional advanced treatment technologies, and the removal of low phosphorus concentration is complicated and expensive. This study proposes application of a simple and recyclable adsorbent to remove low-concentration phosphorus from water. The removal efficiency of phosphorus from low-strength synthetic wastewater was investigated and the adsorption mechanism was analyzed. When the initial phosphorus concentration was 2.0 mg/L, the phosphorus adsorption capacity of Ca-GAT increased to 0.891 mg/g from 0.074 mg/g for GAT at 298 K and pH of 7. Phosphorus adsorption on Ca-GAT performs well when the solution pH is in the range of 5–10, and it is not conducive to the adsorption reaction when the solution pH exceeds 11. The competing anions (such as NO3−, SO42−, HCO3− and F−) existed, Ca-GAT still performed better in removing phosphorus. Then, the saturated absorbents could be effectively regenerated with a 0.5 mos/L NaOH solution, while desorption efficiency was reduced from 97.11% to 33.06% after fifth regeneration cycle. Finally, Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) analysis demonstrated that the Ca2+ content on the Ca-GAT surface played an important role in capturing phosphate ions from wastewater. Phosphorus was mainly removed via the formation of Ca-phosphorus precipitation. To some extent, ligand exchanges of CO32− and OH- with HPO42− and H2PO4− were also beneficial for phosphorus removal. The present work shows that attapulgite has sustainable and beneficial potential in the removal of low-strength phosphorous in wastewater, and the phosphorus loaded adsorbent can be used in the agriculture as slow-release fertilizer.

Start-up of mainstream anammox process through inoculating nitrification sludge and anammox biofilm: Shift in nitrogen transformation and microorganisms

The feasibility of starting up mainstream single-stage partial nitrification-anammox (SPNA) system by inoculating nitrification sludge and anammox biofilm was investigated. The SPNA system treating low-strength synthetic wastewater was rapidly started up with TN removal efficiency of 88.5 ± 1.8% and effluent nitrate concentration of 7.2 ± 1.2 mg/L. Both the abundance and maximum activity of nitrite oxidizing bacteria (NOB) in flocs decreased obviously. Interestingly, the abundance of anaerobic ammonium oxidizing bacteria (AnAOB) in flocs increased from 0.213% to 0.346% despite the sludge retention time (SRT) of flocs decreased to 60 days, the AnAOB in biofilm was 0.434%. That meant AnAOB gradually enriched in flocs and accounted for a fairly high proportion. The inhibition of NOB, partial denitrification and increased aerobic_chemoheterotrophy function in flocs might be the main reasons for AnAOB enrichment. The possibility of simultaneous fermentation, partial denitrification and anammox reaction was predicted in biofilm, further improving the stability of the system.

Facultative-like anaerobic packed bed reactor treating low strength wastewater: microbial community and energy balance appraisements

This study explored the microbial community and the energy requirement of an anaerobic packed bed reactor (APBR) treating a low-strength synthetic wastewater (200 mg COD/L). The APBR was run with different hydraulic retention times (HRTs) and temperatures. Results show that the COD removal decreased from 89 to 46% when the HRTs and the temperature were both gradually reduced to 1 h and 20°C. Meanwhile, the methane yield decreased from 0.386 to 0.232 g COD/g TCODconsumed with the decreasing temperature from 35 to 20°C at 1-h HRT. This low methane production was associated with a low relative abundance of 0.575–0.628% for the archaea group in genus level. Genus Methanosaeta with 0.307–0.388% relative abundance represented 53–62% of the archaea group whereas facultative Trichococcus with 7.3–11.3% relative abundance was dominant in the microbial consortia. Candidatus Moduliflexus found was the second largest microbial population with 4.2–6.1% relative abundance. This facultative environment was observed in the APBR, resulting in 18–37% COD unbalanced. The energy appraisement resolved that the total electrical energy required for the APBR was consistent at 4.192 × 10−3 kWh/m3 at 20–35°C to yield the net energy ratio of 5.97–15.29. The facultative-like APBR treated the low strength wastewater efficiently while the energy input was balanced by its self-produced methane energy.

Construction waste as substrate in vertical subsuperficial constructed wetlands treating organic matter, ibuprofenhene, acetaminophen and ethinylestradiol from low-strength synthetic wastewater

This study aimed to evaluate the removal of chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN), total ammonia nitrogen (TAN), total phosphorus (TP), ibuprofen, acetaminophen and ethinylestradiol of synthetic effluent simulating low-strength sewage by sequencing-batch mode constructed wetlands (CWs). To verify the feasibility of using a floating macrophyte in CWs and compare different substrates, three CWs containing light expanded clay aggregates (CWL), expanded clay with porcelain tiles (CWLP) and bricks (CWB) were planted with Pistia stratiotes. The results showed that CWB achieved the highest removals of TKN (78%), TAN (70%) and TP (46%), and CWLP achieved the highest COD removal (75%). LECA favored the removal of ibuprofen (92%, p < 0.05) when compared to bricks (77%), probably by the combination of biodegradation and sorption in the systems. The highest acetaminophen removal (71% to 96%) was observed in CWL, probably via biodegradation, but no significant differences were found between the CWs (p > 0.05). Ethinylestradiol was removed 76% in CWLP and 73% in CWB, both differing statistically from CWL (p < 0.05), demonstrating that brick and the combination of clay with porcelain were better than just clay in this hormone removal. After 188 days of operation, P. stratiotes was able to uptake nitrogen and phosphorus of approximately 0.28 g and 0.25 g in CWL, 0.33 g and 0.21 g CWLP, and 0.22 g and 0.09 g in CWB of, respectively. Adsorption of nitrogen and phosphorus onto the substrates was 0.48 g and 6.84 g in CWL, 0.53 g and 5.69 g in CWLP, and 0.36 g and 10.18 g in CWB, respectively. The findings on this study suggest that adsorption was possible the main process for TP removal onto the evaluated substrates whereas microbial activity was the most probable mechanism for TN removal in the evaluated CW systems.

Kinetic evaluation of a partially packed upflow anaerobic fixed film reactor treating low-strength synthetic rubber wastewater

A bench-scale model of a partially packed upflow anaerobic fixed film (UAF) reactor was set up and operated at five different hydraulic retention times (HRTs) of (17, 14, 10, 8, and 5) days. The reactor was fed with synthetic rubber wastewater consisting of a chemical oxygen demand (COD) concentration of 6355–6735 mg/L. The results were analyzed using the Monod model, the Modified Stover-Kincannon models, and the Grau Second-Order Model. The Grau Second-Order model was found to best fit the experimental data. The biokinetic constant values, namely the growth yield coefficient (Y) and the endogenous coefficient (Kd) were 0.027 g VSS/g COD and 0.1705 d−1, respectively. The half-saturation constant (Ks) and maximum substrate utilization rate (K) returned values of 84.1 mg/L and 0.371 d−1, respectively, whereas the maximum specific growth rate of the microorganism (μmax) was 0.011 d−1. The constants, Umax and KB, of the Stover-Kincannon model produced values of 6.57 g/L/d and 6.31 g/L/d, respectively. Meanwhile, the average second-order substrate removal rate, ks(2), was 105 d−1. These models gave high correlation coefficients with the value of R2 = 80–99% and these indicated that these models can be used in designing UAF reactor consequently predicting the behaviour of the reactor.

Permeate Flux and Rejection Behavior in Submerged Direct Contact Membrane Distillation Process Treating a Low-Strength Synthetic Wastewater

The effects of operational conditions such as permeate recirculation velocity, mixing intensity, and trans-membrane temperature on the performances of hydrophobic polyethylene (PE) hollow-fiber membrane were investigated by operating the submerged direct contact membrane distillation (SDCMD) process treating a synthetic low-strength wastewater. Permeate flux of the membrane increased with increasing a permeate recirculation velocity through the fiber lumen. However, the effectiveness was less pronounced as the velocity was higher than 0.5 m/s. Increasing rotational speed to 600 rpm, which can lead to mixing intensity from a bulk wastewater toward hollow-fiber membrane, enhanced permeate flux. Feed temperature played a more significant role in enhancing permeate flux rather than a permeate temperature under constant trans-membrane temperature. The SDCMD process treating a synthetic low-strength wastewater achieved an excellent rejection efficiency which is higher than 97.8% for both chemical oxygen demand (CODCr) and total phosphorus (T-P) due to the hydrophobic property of membrane material which can allow water vapor through membrane. However, the rejection efficiency of the ammonia nitrogen (NH3-N) was relatively low at about 87.5% because ammonia gas could be volatized easily through membrane pores in SDCMD operation. In a long-term operation of the SDCMD process, the permeate flux decreased significantly due to progressive formation of inorganic scaling on membrane.

Treatment of domestic wastewater containing phosphate using water treatment sludge through UASB–clariflocculator integrated system

In the present study, treatment of low-strength synthetic wastewater through upflow anaerobic sludge blanket (UASB)–clariflocculator integrated system was carried out. Synthetic wastewater containing sucrose as a carbon source and phosphate as a nutrient was passed through the UASB reactor followed by clariflocculator. Water treatment sludge (WTS) was used as a coagulant in the clariflocculator. Box–Behnken design methodology with response surface methodology was used for optimizing the parameters including WTS dose, hydraulic retention time (HRT) and pH of UASB reactor. The phosphate removal was considered as a response. The observed values of responses were fitted by using second-order polynomial to compute the model. The suitability of this second-order polynomial model was checked by performing ANOVA test. Fisher’s test was done to analyze the significance of each factor and interactions between each other. With this methodology, the optimum operational condition of integrated system was obtained at 20 g/L as a WTS dose, HRT 7.68 h and pH 9. The UASB–clariflocculator integrated system removed 72.5% of phosphate at this optimum condition, whereas the phosphate removal through UASB reactor alone was obtained in the range of 8–20% only. The results suggested that water treatment sludge can be used as a coagulant to enhance the removal of phosphate from UASB reactor effluent treating low-strength wastewater and integrated system can be considered as a promising alternative of conventional system for the removal of nutrient from the effluent of UASB reactor.

Selective production of volatile fatty acids at different pH in an anaerobic membrane bioreactor

This study investigated the production of major volatile fatty acid (VFA) components in an anaerobic membrane bioreactor (AnMBR) to treat low-strength synthetic wastewater. No selective inhibition was applied for methane production and solvent-extraction method was used for VFA extraction. The results showed acetic and propionic acid were the predominant VFA components at pH 7.0 and 6.0 with concentrations of 1.444 ± 0.051 and 0.516 ± 0.032 mili-mol/l respectively. At pH 12.0 isobutyric acid was the major VFA component with a highest concentration of 0.712 ± 0.008 mili-mol/l. The highest VFA yield was 48.74 ± 1.5 mg VFA/100 mg CODfeed at pH 7.0. At different pH, AnMBR performance was evaluated in terms of COD, nutrient removal and membrane fouling rate. It was observed that the membrane fouled at a faster rate in both acidic and alkaline pH conditions, the slowest rate in membrane fouling was observed at pH 7.0.

Kinetics of aerobic granular sludge treating low-strength synthetic wastewater at high dissolved oxygen

ABSTRACT Three parallel reactors (i.e. R1–R3) were operated with 340 mg-COD L−1, 42 mg-TN L−1, and 7 mg-TP L−1 at 20 ± 1°C. A mature granular sludge developed in 40 d and was stable for the 120 d experimentation period at an average food to microorganism ratio of 0.25 ± 0.08 g-COD g-VSS−1 d−1. Reactor biomass had higher inorganic content (i.e. 0.78–0.80 g-VSS g-TSS−1) than effluent biomass (i.e. 0.88–0.92 g-VSS g-TSS−1). Average granule diameter was 0.7–1.0 mm. Maximum phosphorus uptake and release rates averaged 4 ± 3 and 4 ± 2 mg-P g-VSS−1 h−1, respectively. Maximum observed nitrification rates averaged 1.9 ± 0.6 mg-N g-VSS−1 h−1. Phosphorus kinetics were similar between R1–R3 (i.e. P = 0.5309–0.6870) while nitrification kinetics varied significantly (i.e. P = 0.0002) even though conditions were the same. Effluent phosphate was on average 0.2 ± 0.4 mg-P L−1 while total inorganic nitrogen removal averaged 60 ± 10% resulting in an average effluent of 17 mg-N L−1. Aerobic granular sludge was capable of reliable nutrient removal from low-strength wastewater without volatile fatty acid source and at high dissolved oxygen concentrations.

Realizing stable operation of anaerobic ammonia oxidation at low temperatures treating low strength synthetic wastewater

The low activity of Anammox bacteria at low temperatures and competition from nitrite oxidation bacteria (NOB) when treating low strength wastewater have been major bottlenecks in implementing Anammox in mainstream wastewater treatment. By intermittent high strength feeding (IHSF) and stepwise temperature reduction, stable operation of a granular Anammox reactor was realized at low temperatures (down to 15°C) for 28days when treating low strength synthetic wastewater. The nitrogen loading rate reached 1.23–1.34kgN/m3/day, and the total nitrogen removal rate reached 0.71–0.98kgN/m3/day. The IHSF enriched the Anammox sludge in high strength cycles and compensated for sludge loss in low strength cycles, and the high concentration of ammonium in high strength cycles inhibited NOB. The 16SrRNA gene sequencing results revealed that Candidatus Kuenenia was predominant in the reactor at low temperatures.

Enhanced nitrogen removal in an aerobic granular sequencing batch reactor performing simultaneous nitrification, endogenous denitrification and phosphorus removal with low superficial gas velocity

An aerobic granular simultaneous nitrification, endogenous denitrification and phosphorus removal (SNDPR) system was configured for simultaneous carbon and nutrients removal fed with low-strength synthetic wastewater (0.3kgCOD/(m3·d)). The SNDPR system was operated on an anaerobic/oxic/anoxic (AOA) mode with a gradually dropping superficial gas velocity (SGV) from 0.17, 0.11 to 0.04cm/s. Long term operation over 120days revealed decreasing SGV resulted in poorer settleability and microbial activity as well as larger particle sizes, which were in great linear correlations with the sharp decrease of protein/polysaccharides (PN/PS). Excellent removal of chemical oxygen demand (COD) and phosphorus were achieved during the whole process, while enhanced nitrogen removal was observed by dropping the SGV. Both simultaneous nitrification and denitrification rate (SND) and nitrite accumulation rate (NUR) increased significantly, as with the removal efficiency for nitrogen. Illumina MiSeq pyrosequencing displayed glycogen-accumulating organisms (GAOs) Candidatus_Competibacter predominated the SDNPR system, while the PAOs Candidatus_Accumulibacter grew notably with decreased SGV. Lower SGVs favored the enrichment of ammonia-oxidizing bacteria (AOB) while suppressed the accumulation of nitrite-oxidizing bacteria (NOB). This study might contribute to the application of SNDPR system for simultaneous carbon, nitrogen and phosphorus removal.

Treatment of low-strength wastewater at mesophilic and psychrophilic conditions using immobilized anaerobic biomass

An anaerobic immobilized bio-plates reactor (AnIBPR) of effective volume of 14.5L and bio-plate packing ratio of 27.5% was used to treat low-strength synthetic wastewater (COD of 400mg/L) at a hydraulic retention time (HRT) of 16h. Treatment performance was investigated at different temperatures. The results showed that the reactor AnIBPR achieved COD removal of 86–92% at mesophilic (35°C and 25°C) and psychrophilic (15°C) conditions. Dissolved methane (CH4) was found to be oversaturated in the reactor (saturation factor of 1.03–1.21), increasing with decreasing temperature. Increased dissolved CH4 content at 15°C, albeit at decreased production, was attributed to significant mass transfer limitation due to lower KLa at low temperature, resulting in oversaturation of dissolved CH4. Increasing treatment temperature to mesophilic conditions led to increased reaction rates and yields. At steady state, gas-phase CH4 content was 75–83% and the overall yield was 0.22–0.26L/gCOD removed. Steady-state volatile fatty acids (VFAs) were measured at 3.3–12mgCOD/L, small amounts that were unlikely to hamper treatment performance.

Effects of the residual ammonium concentration on NOB repression during partial nitritation with granular sludge

Partial nitritation was stably achieved in a bench-scale airlift reactor (1.5L) containing granular sludge. Continuous operation at 20 °C treating low-strength synthetic wastewater (50 mg N-NH4+/L and no COD) achieved nitrogen loading rates of 0.8 g N-NH4+/(L·d) during partial nitritation. The switch between nitrite-oxidizing bacteria (NOB) repression and NOB proliferation was observed when ammonium concentrations in the reactor were below 2–5 mg N-NH4+/L for DO concentrations lower than 4 mg O2/L at 20 °C. Nitrospira spp. were detected to be the dominant NOB population during the entire reactor operation, whereas Nitrobacter spp. were found to be increasing in numbers over time. Stratification of the granule structure, with ammonia-oxidizing bacteria (AOB) occupying the outer shell, was found to be highly important in the repression of NOB in the long term. The pH gradient in the granule, containing a pH difference of ca. 0.4 between the granule surface and the granule centre, creates a decreasing gradient of ammonia towards the centre of the granule. Higher residual ammonium concentration enhances the ammonium oxidation rate of those cells located further away from the granule surface, where the competition for oxygen between AOB and NOB is more important, and it contributes to the stratification of both populations in the biofilm.

Cathodic fluidized granular activated carbon assisted-membrane bioelectrochemical reactor for wastewater treatment

Abstract A membrane bioelectrochemical reactor (MBER) is a system integrating membrane filtration into microbial fuel cells. To control membrane fouling, fluidized granular activated carbon (GAC) was applied to the cathodic compartment of an MBER, which was examined for contaminant removal and electricity generation with low or medium strength synthetic wastewater. The MBER was operated for more than 160 days and achieved nearly 100% removal of organic compounds, regardless of presence/absence of GAC. However, fluidized GAC alleviated the membrane fouling issue and maintained transmembrane pressure (TMP) between 10 and 15 kPa with 24 g of GAC. The presence of GAC also enhanced current generation from 200.3 to 256.0 A m −3 , because some GAC might have functioned as a part of the cathodic electrode through physical contact with the electrode during fluidization. A higher aeration intensity could benefit both membrane fouling control (via scouring effect) and electricity generation (via oxygen supply), but required a higher energy demand. The energy consumption of the MBER including pumping and aeration was estimated to be 0.38 kWh m −3 or 0.25 kWh kgCOD −1 , lower than that of conventional membrane bioreactors (MBRs). Those results encourage further investigation and development of the MBER technology to treat wastewater in an energy efficient way.

Nitrous oxide emissions from an aerobic granular sludge system treating low-strength ammonium wastewater

Aerobic granular sludge is a promising technology in wastewater treatment process. Its special microorganism structure could make the emissions of greenhouse gas nitrous oxide (N2O) more complicated. This study investigated the N2O emissions from a batch-fed aerobic granular sludge system during nitrification of low-strength synthetic ammonium wastewater. The N2O emission was 2.72±0.52% of the oxidized ammonium during the whole anoxic-oxic sequencing batch reactor (SBR) cycle. Under nitrification batch test with sole ammonium substrate (50mgN/L), N2O emission factor was 1.82% (N2ON/NH4+-Nox) and ammonia-oxidizing bacteria (AOB) was the responsible microorganism. The presence of high ammonium concentration (or high ammonium oxidation rate (AOR)) and accumulation of nitrite would lead to significant N2O emissions. AOB denitrification pathway was speculated to contribute more to the N2O emissions under nitrification conditions. While under simultaneous nitrification and denitrification condition with carbon source of 500mg COD/L, the N2O emission factor increased to 2.76%. Both AOB and heterotrophic denitrifiers were responsible for N2O emission and heterotrophic denitrification enhances N2O emission. Step feeding of organic carbon source declined N2O emission factor to 1.60%, which underlined the role of storage substance consumption in N2O generation during denitrification.

Biosorption of Zn(II) in High and Low Strength Synthetic Wastewater by Watermelon Rind (&lt;i&gt;Citrullus lanatus&lt;/i&gt;)

The heavy metal contain in the industrial wastewater can cause a pollution towards the environment and human due to its toxicity. Therefore extensive studies were conducted for the heavy metal removal. This study was conducted under several conditions by varying pH, biosorbent dosage, initial wastewater concentration and contact time. The results revealed that optimum pH, for high strength synthetic wastewater was 8.0 meanwhile for low strength synthetic wastewater was 7.0. Both high and low strength synthetic wastewater was optimum at 30 minutes of contact time with 1.5g and 0.02g of bisorbent dosage respectively. Meanwhile, the optimum initial metal concentration for high and low strength synthetic wastewater was 400ppm and 1ppm respectively. The results had proven that watermelon rind is able to treat wastewater with high and low concentration of metal.

Partial nitrification in sequencing batch reactors treating low ammonia strength synthetic wastewater.

Sequencing batch reactors fed with low ammonium strength synthetic wastewater under C/N ratios of 0.5, 1.5, and 3.0 were used to investigate the transition from full to partial nitrification. Two strategies for establishing partial nitrification, aeration duration control and process parameter control, were compared. The effect of C/N ratio on nitrite accumulation was also evaluated. Results showed that partial nitrification established by controlling aeration duration presented better performance with higher nitrite accumulation. An increase of C/N ratio helped nitrite accumulation; however, non-filamentous bulking of sludge happened at high C/N ratio. Based on mass balances for nitrogen, results for nitrogen during full and partial nitrification were distinct from one another. For low C/N ratio, during full nitrification, almost 100% of NH(4+)-N was oxidized to NO(3-)-N without nitrogen loss; however, nitrogen loss increased obviously during partial nitrification, which indicated that dissolved oxygen concentration and C/N ratio influenced nitrogen loss significantly during nitrification.