Sludge Treatment System Research Articles

Enhancing Biodegradability of Refractory Aromatics in Wastewater: Pretreatment with Elemental Iron

Chlorinated aromatics, nitroaromatics, and azoaromatics are widely used in industry. As a result, these compounds are commonly present in industrial wastewater. Aerobic biological treatment processes are often inefficient for wastewaters containing these organic pollutants because most of these aromatic compounds are resistant to aerobic degradation. The goal of this research is to investigate the feasibility of elemental iron to pretreat wastewater through reduction of the azo and nitro functions, thus making these compounds more biodegradable prior to entering biological treatment processes, such as activated sludge. The experimental approach involved a series of batch reduction experiments to test the treatability, via chemical reduction, of a suite of compounds (nitrobenzene, 2,4-dinitrotoluene, orange G, orange II, orange IV, orange I, 1,2,4-trichlorobenzene, and pentachlorophenol) as well as the effects that various synthetic wastewater components would have on reduction rates. Once reduction products were identified in the batch reduction experiments, they were tested for their aerobic biodegradability through batch biodegradation and respirometric studies. A set of column experiments to examine iron life span were the final precursor to design and operation of a bench-scale integrated iron column-activated sludge treatment system for azo dyes. Results from batch reduction experiments indicate that azo dyes and nitroaromatics are rapidly transformed to their reduced counterparts. In all cases, the pretreatment of recalcitrant compounds via reduction with elemental iron enhanced their aerobic biodegradability This title belongs to WERF Research Report Series ISBN: 9781843396765 (eBook)

Understanding the distribution, degradation and fate of organophosphate esters in an advanced municipal sewage treatment plant based on mass flow and mass balance analysis

Although organophosphate esters (OPEs) in the ambient environment are from sewage treatment plants due to the discharge of effluent and application of sludge, the distribution, degradation and fate of OPEs in advanced municipal sewage treatment plants remain unclear. This work focused on the use of mass flow and mass balance analysis to understand the behaviors and fate of 14 OPEs in an advanced municipal sewage treatment plant. OPEs were detected in all sewage water and sludge samples with total OPEs (ΣOPEs) concentrations of 1399±263ng/L in raw sewage aqueous phase, 833±175ng/L in tertiary effluent aqueous phase, and 315±89ng/g dry weight in dewatered sludge. The dissolved concentrations of ΣOPEs significantly decreased during biological treatment, whereas negligible decrease was observed in mechanical and physical-chemical treatments. For individual OPE, the chlorinated tris(2-chloroethyl) phosphate (TCEP) and tris(2-chloroisopropyl) phosphate (TCPP) did not decrease but increased during both biological treatment and physical-chemical treatment. Mass flow analysis indicated the total removal efficiency of ΣOPEs in aqueous phase was 40.5%, and the polarity-specific removal efficiencies for individual OPE were positively related to their solid-water partition coefficients (Kd). Furthermore, mass balance results showed that 53.1% and 6.3% of the initial OPE mass flow were eventually transferred to the effluents and dewatered sludge, respectively, while the remaining 39.9% and 0.7% were lost due to biodegradation and physical-chemical treatment, respectively. It was indicated that the activated sludge treatment system with anaerobic/anoxic/aerobic bioreactors was a major factor in the removal of OPEs from the raw sewage, while transfer to dewatered sludge governed by hydrophobic interactions was limited during the sewage treatment. Meanwhile, the degradation difference of OPEs in activated sludge treatment was more related with their molecular structure over their hydrophobicity.

Response to shock load of engineered nanoparticles in an activated sludge treatment system: Insight into microbial community succession.

The environmental impacts of the use of engineered nanoparticles (NPs) remain unclear and have attracted increasing concern worldwide. Considering that NPs eventually end up in wastewater treatment systems, the potential impact of ZnO and TiO2 NPs on the activated sludge was investigated using laboratory-scale sequencing batch reactors (SBRs). Short-term (24 h) exposure to 1, 10 and 100 mg/L shock loads of NPs reduced the oxygen uptake rate of the activated sludge by 3.55%-12.51% compared with the controls. In our experiment, the toxicities of TiO2 NPs were higher than those of ZnO NPs as reflected in the inhibition of oxygen utilization in the activated sludge. However, both the short-term (24 h) and long-term (21 days) exposure to ZnO and TiO2 NPs did not adversely affect the pollutant removal of the SBRs. Furthermore, the polymerase chain reaction-denaturing gel gradient electrophoresis revealed that the microbial community did not significantly vary after the short-term exposure (24 h) to 1, 10 and 100 mg/L shock loads of NPs; however, the cluster analysis in our experiment revealed that the slight difference caused by the NPs largely depended on exposure time rather than on NP type and NP concentration. The long-term exposure (13 days) to 10 mg/L shock load of ZnO or TiO2 NPs caused no substantial microbial community shifts in the activated sludge. The microbial diversity also showed no significant change when exposed to NPs as revealed by the Shannon-Wiener index.

Effect of iron–manganese–sepiolite as heterogeneous Fenton-like catalyst on the performance and microbial community of anaerobic granular sludge treatment system

Both short-term and long-term exposure experiments have been carried out to investigate the influence of iron (Fe)–manganese (Mn)–sepiolite, as a heterogeneous Fenton-like catalyst, on the performance and microbial community of anaerobic granular sludge. During the short-term exposure experiments, chemical oxygen demand (COD) removal efficiency decreased from 73.1% to 64.1% with the presence of 100mg/L of catalyst. However, long-term exposure to the catalyst did not significantly affect the COD removal efficiency (81.8%) as compared to the control (83.5%). Meanwhile, the absorption peaks of coenzyme F420 in extracellular polymeric substances (EPS) of sludge samples were remarkable by excitation–emission matrix (EEM) fluorescence spectra. After long-term exposure, the presence of the catalyst increased secretions of EPS from 83.7mg/g VSS to 89.1mg/g VSS. Further investigations with high throughput sequencing indicated that the abundance of Methanosaeta increased from 57.7% to 70.4% after long-term exposure. In bacterial communities, Proteobacteria, Firmicutes, and Synergistetes were predominant.

Pilot-scale study of sludge pretreatment by microwave and sludge reduction based on lysis–cryptic growth

To evaluate the performance of microwave (MW)-chemical hybrid sludge treatment system, a pilot scale MW disintegration unit (treatment capacity of 500L/d) was constructed. The results showed that organic matter, nitrogen, and phosphorus were effectively released from the MW-pretreated sludge. The values of COD released were 15.91%, 15.07%, 13.83%, 19.35%, and 15.07% for the MW, MW-acid, MW-alkali, MW-H2O2, and MW-H2O2-alkali treatment processes, respectively. Additionally, for a wastewater treatment system with a capacity of 200m3/d, when coupled with a MW sludge pretreatment unit, the sludge production and sludge yield were greatly reduced by 38.60% and to 0.35kg VSS/kg CODconsumed, respectively. The total operating cost of the lysis–cryptic growth system was 13.64% lower than that of the CAS system without a MW unit.

Drinking Water Supply and Sanitation: A Typical Syndrome in Sub-Urban Rural Areas: Require Scientific and Technological Intervention

The population and industrial growths are demanding for sustainable and safe drinking water and waste disposal in rural and urban belts. Deficiency and lack of fresh water supply and sewage disposal/treatment affects the health and hygiene of household, community dwellers and local/regional environment. The paper highlights the problems around Farukh Nagar of Gurgaon District in Haryana and suggests for scientific and technological study to address the issue. Preliminary field visit and study show the gravity of problem and possible reasons. However, detailed study is required adopting scientific and technological viable strategy including methodology, questionnaire based interaction with beneficiaries and agencies to collect stratified socio-economic and technical primary and secondary details/records, people perceptions and experiences, Ground water details (level, yield, point source and quality fluctuations), Surface water source, rainfall, water supply system/parameters, population and growth, waste water and sludge production, treatment and disposal system, recharge and outfall zone in the study/nearby areas, etc. Further, analysis of data employing hydrological/hydraulic software, testing/verification of quality parameters with Indian and international standards, physical models, workshops among beneficiaries and user agencies addressing the points of innovation to implement viable and sustainable water supply and sewage disposal plans are needed.

Potential of a bacterial consortium to degrade azo dye Disperse Red 1 in a pilot scale anaerobic–aerobic reactor

The textile industry is the largest consumer of azo dyes and activated sludge treatment systems typically used to remove them are frequently inefficient, resulting in significant quantities of these compounds adsorbed in the sludge or released into water bodies. The aim of this study was to evaluate the biodegradation of the commercial azo dye Disperse Red 1 in a pilot scale anaerobic–aerobic reactor inoculated by a microbial consortium selected for its capacity to degrade azo dyes. Dye decolorization (80%) occurred in 60h in the anaerobic reactor and 92% COD (chemical oxygen demand) was removed as measured in the treated effluent. LC–ESI-MS/MS of the treated effluent showed the formation of a reduced azo bond and azo bond cleavage and subsequent degradation products. Aromatic amines produced by the cleavage of the azo bond were not detected. Toxicity tests performed with Daphnia similis and Hydra attenuata in the treated effluent showed that the toxicity was reduced significantly. Mutagenicity, evaluated using the Salmonella/microsome Ames test, found the untreated dye medium was only mutagenic toward Salmonella strain YG1041. However after treatment, only marginal mutagenicity was observed. These results indicate the bacterial consortium was effective in biodegrading Disperse Red 1 and also reducing the toxicity and mutagenicity and may represent a promising application for dyes biodegradation.

Application of Novel Amino-Functionalized NZVI@SiO2 Nanoparticles to Enhance Anaerobic Granular Sludge Removal of 2,4,6-Trichlorophenol.

A novel amino-functionalized silica-coated nanoscale zerovalent iron (NZVI@SiO2-NH2) was successfully synthesized by using one-step liquid-phase method with the surface functionalization of nanoscale zerovalent iron (NZVI) to enhance degradation of chlorinated organic contaminants from anaerobic microbial system. NZVI@SiO2-NH2 nanoparticles were synthesized under optimal conditions with the uniform core-shell structure (80–100 nm), high loading of amino functionality (~0.9 wt%), and relatively large specific surface area (126.3 m2/g). The result demonstrated that well-dispersed NZVI@SiO2-NH2 nanoparticle with nFe0-core and amino-functional silicon shell can effectively remove 2,4,6-trichlorophenol (2,4,6-TCP) in the neutral condition, much higher than that of NZVI. Besides, the surface-modified nanoparticles (NZVI@SiO2-NH2) in anaerobic granule sludge system also showed a positive effect to promote anaerobic biodechlorination system. More than 94.6% of 2,4,6-TCP was removed from the combined NZVI@SiO2-NH2-anaerobic granular sludge system during the anaerobic dechlorination processes. Moreover, adding the appropriate concentration of NZVI@SiO2-NH2 in anaerobic granular sludge treatment system can decrease the toxicity of 2,4,6-TCP to anaerobic microorganisms and improved the cumulative amount of methane production and electron transport system activity. The results from this study clearly demonstrated that the NZVI@SiO2-NH2/anaerobic granular sludge system could become an effective and promising technology for the removal of chlorophenols in industrial wastewater.

Sludge quality after 10-20years of treatment in reed bed systems.

The effect on the environment of the operation of sludge treatment in reed beds (STRB) system is seen as quite limited compared to traditional sludge treatment systems such as mechanical dewatering, drying and incineration with their accompanying use of chemicals and energy consumption. There are several STRB systems in Denmark receiving sludge from urban wastewater treatment plants. Stabilization and mineralization of the sludge in the STRB systems occur during a period between 10 and 20years, where after the basins are emptied and the sludge residue typically is spread on agricultural land. In the present study, the sludge residue quality after treatment periods of 10-20years from four Danish STRBs is presented. After reduction, dewatering and mineralization of the feed sludge (dry solid content of 0.5-3%) in the STRB systems, the sludge residue achieved up to 26% dry solid, depending on the sludge quality and dimensioning of the STRB system. The concentration of heavy metals and hazardous organic compounds in the sludge residue that are listed in the Danish and EU legislation for farmland application of sludge was below the limit values. The nitrogen and phosphorus concentrations as an average in the sludge residue were 28 and 36g/kg dry solid (DS), respectively. In addition, mineralization on average across the four STRB systems removed up to 27% of the organic solids in the sludge. The investigation showed that the sludge residue qualities of the four STRBs after a full treatment period all complied with the Danish and European Union legal limits for agricultural land disposal.

Effect of short-term exposure of selected aromatic nitrogen compounds on wastewater treatment.

The biodegradation of melamine and p-nitrophenol (PNP) and their impact on wastewater treatment was evaluated after a short-term individual chemical loading in activated sludge treatment systems. Melamine was not degraded and quickly washed out of the system. PNP was degraded, but it led to a prolonged period of nitrification inhibition and deterioration of effluent quality. Both melamine and PNP loadings increased the effluent nitrogen concentrations, with their main contributors being melamine and NH4+, respectively. Nitrosomonas and Nitrospira were dominant in the activated sludge. Melamine did not affect the nitrifying assemblages, whereas PNP led to a reduced Nitrosomonas population size and complete washout of Nitrobacter. The results suggest that melamine is an inert compound if it enters the treatment facility for a short duration. Although the short-term exposure of melamine or PNP decreased effluent water quality,the impact of such aromatic nitrogen compounds on wastewater treatment performance may vary significantly. Water

Real scale environmental monitoring of zoonotic protozoa and helminth eggs in biosolid samples in Brazil.

Biosolid is the product of the activated sludge treatment system and its final disposition is subject of ongoing discussion as this residue can therefore harbor a great number and variety of pathogens. This study was aimed to (1) monitor the presence of Giardia and Cryptosporidium in biosolid samples from a treatment plant in Campinas, SP, Brazil, (2) observe Giardia cyst wall morphological integrity in treated samples using scanning electron microscopy (SEM) and (3) verify the presence and viability of helminth eggs. Cysts were present in 33.3% of the samples, whereas oocysts were detected in 8.3%. Viable Ascaris sp. Toxocara sp. and similar to Trichuris sp. eggs were found through the use of Mexican Official Norm. Results demonstrate the difficulties inherent in working with biosolid as factors such as temperature, ionic strength and pH influenced the recovery of cysts and oocysts. Pores and ruptures were not observed in cyst wall visualized by SEM following 45days of exposure to sunlight, only minimal morphological changes. These observations emphasize both the importance of adequate treatment of sewage sludge and the need to develop appropriate techniques for the detection of Giardia and Cryptosporidium in this type of sample. This is the first time that a study was done in a real scale for biosolid samples in determining the presence of pathogenic protozoa as Giardia and Cryptosporidium in Brazil, and also observed minimal cyst wall damage after sunlight treatment.

Characterization of cefalexin degradation capabilities of two Pseudomonas strains isolated from activated sludge

Pharmaceuticals have recently been regarded as contaminants of emerging concern. To date, there is limited knowledge about antibiotic-degrading microorganisms in conventional activated sludge treatment systems and their characteristics toward antibiotic degradation especially in the presence of a pharmaceutical mixture. As such, antibiotic-degrading microorganisms were investigated and isolated from the activated sludge, and their degradation capabilities were evaluated. Two strains of cefalexin-degrading bacteria CE21 and CE22 were isolated and identified as Pseudomonas sp. in the collected activated sludge. Strain CE22 was able to degrade over 90% of cefalexin, while CE21 was able to remove 46.7% of cefalexin after incubation for 24h. The removal efficiency of cefalexin by CE22, different from that of CE21, was not significantly affected by an increase in cefalexin concentration, even up to 10ppm, however the presence of 1ppm of other pharmaceuticals had a significant effect on the degradation of cefalexin by CE22, but no significant effect on CE21. The degradation product of cefalexin by the two strains was identified to be 2-hydroxy-3-phenyl pyrazine. Our results also indicated that CE21 and CE22 were able to degrade caffeine, salicylic acid and chloramphenicol. Moreover, CE21 was found to be capable of eliminating sulfamethoxazole and naproxen.

How does the entering of copper nanoparticles into biological wastewater treatment system affect sludge treatment for VFA production

Usually the studies regarding the effect of engineered nanoparticles (NPs), which are released to wastewater treatment plant, on sludge anaerobic treatment in the literature have been conducted by directly adding NPs to sludge treatment system. Actually, NPs must enter into the wastewater treatment facility from influent before sludge being treated. Thus, the documented results can not reflect the real situations. During sludge anaerobic treatment for producing volatile fatty acids (VFA, the preferred carbon source for wastewater biological nutrient removal), it was found in this study that the entering of CuNPs to biological wastewater treatment system had no significant effect on sludge-derived VFA generation, while direct addition of CuNPs to sludge fermentation reactor caused a much lower VFA production, when compared to the control test. Further investigation revealed that the entering of CuNPs into wastewater biological treatment system improved sludge solubilization due to the decline of sludge particle size and the increase of sludge microorganism cells breakage. In addition, there was no obvious influence on hydrolysis, while significant inhibition was observed on acidification, resulting in the final VFA production similar to the control. When CuNPs were directly added to the fermentation system, the solubilization was little influenced, however the hydrolysis and acidification were seriously inhibited, causing the ultimate VFA generation decreased. Therefore, selecting proper method close to the real situation is vital to accurately assess the toxicity of nanoparticles on sludge anaerobic fermentation.

Development of a down-flow hanging sponge reactor for the treatment of low strength sewage

The process performance of a down-flow hanging sponge (DHS) reactor for treating low strength sewage (biochemical oxygen demand (BOD) 20-50 mg/L) was investigated in Bangkok, Thailand. The hydraulic retention time (HRT) was set at 4 h during the start-up period and was reduced to 1.5 h in a stepwise manner. Throughout the 300-day operational period, the DHS reactor shows high performance with respect to the removal of total suspended solid (>90% total suspended solid removal efficiency). No clogging of sponge media was observed in response to the self-digestion phenomena of the biofilm. At a HRT of 1.5 h, the BOD removal efficiency was sufficiently high (about 85%). The pathogen Escherichia coli and other coliform bacteria were removed almost completely as well (removal was 99.4% and 98.1%, respectively). Regarding the retained sludge activity measurement, the nitrite oxidation rate was higher than the ammonium oxidation rate (0.031 and 0.022 gram of nitrogen per gram of volatile suspended solids per day, respectively). In the 300 days of operation, the amount of excess sludge production was negligible. Thus, no sludge treatment system is required. Introduction of the DHS system in developing countries is recommended because this system requires a relatively small area, and has low electricity consumption and operation costs.

Influence of High-Salinity Impact Load on an Integrated Sync Contact Oxidation Process

To solve the problem of high-salt ballast wastewater treatment, biological contact oxidation process by combined packing used to simulate the experimental study. When dissolved oxygen is 5 to 6, water temperature is 18 ~ 20 °C, pH is 7~8 and hydraulic retention time is 48h, the Influence of salinity dips and swells process on sludge treatment system and its effects were investigated. The results showed that salinity shock loads on the system less affected COD removal, after 3-5 days short adaptability run, the system became able to restore effluent water stability. The influence of Salinity swells process on AOB, NOB and denitrifying bacteria was greater than a dip .Salinity plunged produced smaller impact on the total nitrogen removal, while in the salinity swells TN removal reduced from 70.7% to 42%.

Ecophysiology of nitrifying communities in membrane bioreactors

Membrane bioreactors (MBRs) are rapidly becoming the technology of choice over conventional activated sludge treatment systems due to their smaller footprint, reduced sludge production, rapid start-up of biological processes, complete removal of suspended solids and better effluent quality. The retention of sufficient amount of slow-growing nitrifiers makes it feasible for the MBRs to achieve strong tolerance against the shock loads with stable and highly efficient nitrogen removal. Various studies have focused on the ecophysiology of nitrifiers in MBRs as well as their distinctive operational parameters as well as their impact on the selection and activity of nitrifying community. Several techniques have been employed over the years to understand the nitrifying community and their interaction within the MBR system, which led to its modification from the initial design. This review focuses on the identification of optimal operational and environmental conditions for efficient nitrification in MBRs. The advantages and limitations of different techniques employed for investigating the nitrifying communities in MBRs are also emphasized.

Analyzing environmental hotspots of proposed landfill extension and advanced incineration facility in Hong Kong using life cycle assessment

Abstract This paper evaluates the environmental impacts and identifies the hotspots associated with the sub-processes of the proposed landfill extension (LFE) and advanced incineration facility (AIF) for municipal solid waste (MSW) disposal in Hong Kong using life cycle assessment methodology. On the basis of the data collected, assumptions made, and system boundary defined, results show that sub-processes of LFE that provide most burdens on human health and ecosystem quality are biological reactions at landfill cells and sludge collection and treatment system, respectively. Meanwhile, stack discharge system in the AIF has highest impact on human health and ecosystem quality. Overall, the LFE performs more poorly than the AIF in view of human health but vice versa for ecosystem quality. The comparison of the LFE and AIF, with and without energy recovery systems, indicates quantitatively that the energy recovery systems provide benefits in regard to climate change, respiratory inorganics and acidification/eutrophication. Energy recovery in the waste sector could be enhanced through technological improvement and economic incentives. The environmental performances by applying Hong Kong's target emission levels for the stack discharge system in the AIF are also more favorable with respect to human health and ecosystem quality than those of Mainland China's and U.S.EPA standards. This study provides an additional view to the stakeholders in decision making process for pledging a sustainable management of MSW disposal in Hong Kong.

Removal of endocrine-disrupting chemicals and conventional pollutants in a continuous-operating activated sludge process integrated with ozonation for excess sludge reduction

Sludge ozonation is considered as a promising technology to achieve a complete reduction of excess sludge, but as yet its effects on the removal of endocrine-disrupting chemicals (EDCs) and conventional pollutants (i.e., COD, N and P) in the activated sludge process are still unclear. In this study, two lab-scale continuous-operating activated sludge treatment systems were established: one was operated in conjunction with ozonation for excess sludge reduction, and the other was operated under normal conditions as control. The results indicate that an ozone dose of 100mgO3g−1SS led to a zero yield of excess sludge in the sludge-reduction system during a continuous-operating period of 45d. Although ozonation gave a relatively lower specific oxygen uptake rate of activated sludge, it had little effect on the system’s removal performance of COD and nitrogen substances. As a plus, sludge ozonation contributed a little more removal of target EDCs (estrone, 17β-estrodiol, estriol, 17α-ethinylestradiol, bisphenol A, and 4-nonylphenol). However, the total phosphorus removal declined notably due to its accumulation in the sludge-reduction system, which necessitates phosphorus recovery for the activated sludge process.

Filamentous sludge bulking control by nano zero-valent iron in activated sludge treatment systems.

Sludge bulking causes loss of biomass in the effluent and deterioration of effluent water quality. This study explored the use of nano zero-valent iron (NZVI with an average particle size of 55 ± 11 nm) for sludge bulking control. In two Modified Ludzack-Ettinger (MLE) activated sludge treatment systems, a single dose of NZVI at the final concentration of 100 mg Fe per L in the mixed liquor reduced the number of filamentous bacteria Type 021N by 2-3 log units (a reduction of 99.9 and 96.7% in MLE tank #1 and #2, respectively). The side effect of the use of NZVI depended on sludge bulking conditions and biomass concentration. In the system with sludge bulking and significant sludge loss (average biomass concentration of 1022 ± 159 COD mg per L or at the ratio of 0.098 g Fe per g biomass COD), the use of NZVI increased effluent COD, NH4(+)-N and NO2(-)-N concentrations, as also evident with the loss of nitrifying populations and nitrifying activities resulting in more than 40 days to have the full recovery of the activated sludge system. In contrast, in the system with the early stages of bulking and the biomass concentration of 1799 ± 113 COD mg per L (at the ratio of 0.056 g Fe per g biomass COD), the effluent water quality and overall bioreactor performance were only slightly affected for a few days.

Fractionation of wastewater characteristics for modelling of Firle Sewage Treatment Works, Harare, Zimbabwe

Varying conditions are required for different species of microorganisms for the complex biological processes taking place within the activated sludge treatment system. It is against the requirement to manage this complex dynamic system that computer simulators were developed to aid in optimising activated sludge treatment processes. These computer simulators require calibration with quality data input that include wastewater fractionation among others. Thus, this research fractionated raw sewage, at Firle Sewage Treatment Works (STW), for calibration of the BioWin simulation model. Firle STW is a 3-stage activated sludge system. Wastewater characteristics of importance for activated sludge process design can be grouped into carbonaceous, nitrogenous and phosphorus compounds. Division of the substrates and compounds into their constituent fractions is called fractionation and is a valuable tool for process assessment. Fractionation can be carried out using bioassay methods or much simpler physico-chemical methods. The bioassay methods require considerable experience with experimental activated sludge systems and associated measurement techniques while the physico-chemical methods are straight forward. Plant raw wastewater fractionation was carried out through two 14-day campaign periods, the first being from 3 to 16 July 2013 and the second was from 1 to 14 October 2013. According to the Zimbabwean Environmental Management Act, and based on the sensitivity of its catchment, Firle STW effluent discharge regulatory standards in mg/L are COD (<60), TN (<10), ammonia (<0.2), and TP (<1). On the other hand Firle STW Unit 4 effluent quality results based on City of Harare records in mg/L during the period of study were COD (90±35), TN (9.0±3.0), ammonia (0.2±0.4) and TP (3.0±1.0). The raw sewage parameter concentrations measured during the study in mg/L and fractions for raw sewage respectively were as follows total COD (680±37), slowly biodegradable COD (456±23), (0.7), readily biodegradable COD (131±11), (0.2), soluble unbiodegradable COD (40±3), (0.06), particulate unbiodegradable COD (53±3) (0.08), total TKN (40±4) mg/L, ammonia (28±6), (0.68), organically bound nitrogen (12±2), (0.32), TP (15±1.4), orthophosphates (9.6±1.4), (0.64), and organically bound TP (5.4±1.4), (0.36), soluble unbiodegradable TP (0.4±0), (0.03), particulate unbiodegradable TP (0.05±0), (0.003). Thus, wastewater at Firle STW was found to be highly biodegradable suggesting optimisation of biological nutrient removal process will generally achieve effluent regulatory standards compliance. Thus, opportunities for plant optimisation do exist of which modelling with the use of a simulator is recommended to achieve recommended effluent standards in addition to reduction of operating costs.