Water and Wastewater Operations

Tools in this group

• Pounds Formula - lb/day = MGD * mg/L * 8.34, with adjusted product feed at the chemical's purity.
• Filter Loading Rate and Backwash - Loading rate, backwash flow, and rapid-sand vs high-rate category.
• RO Recovery, Concentrate Flow, and Concentration Factor - The reverse-osmosis mass balance an operator sets recovery from: recovery R = permeate / feed, concentrate (reject) flow = feed - permeate, and the concentration factor CF = 1 / (1 - R) is how much the rejected salts pile up in the reject. At 75% recovery (10 gpm feed, 7.5 gpm permeate) the reject is 2.5 gpm and CF = 4, so a 500 mg/L feed leaves about a 2,000 mg/L concentrate; 50% recovery is only CF = 2. Pushing recovery higher shrinks the reject but raises CF sharply, and past the scaling limit of the least-soluble salt the membrane fouls -- antiscalant and the LSI govern that ceiling. The membrane manufacturer's projection software and the state primacy agency (for a public system) govern the design.
• Chlorine Dose to Oxidize Iron and Manganese - The free-chlorine dose to oxidize dissolved iron and manganese ahead of a filter: 0.62 mg Cl2 per mg of ferrous iron, 1.30 mg Cl2 per mg of manganese, plus any other chlorine demand and the free residual to carry; lb/day = dose x flow (MGD) x 8.34. Fe 3.0, Mn 0.5, 0.5 demand, 0.3 residual is a 3.31 mg/L dose, 1.38 lb/day at 0.05 MGD. Iron oxidizes in minutes, but manganese is slow at low pH and usually needs a pH near 8 or a catalytic (greensand / pyrolusite) filter to finish; permanganate or air are alternatives. A dosing estimate; jar tests, the pH, the contact time, and the state primacy agency govern the actual feed.
• Cistern / Storage Reserve Days and Required Volume - The reserve a storage tank carries and the tank a target reserve needs, a straight mass balance: days = usable storage / daily demand, and required volume = daily demand x target days. A 2,500-gal usable cistern at 150 gpd carries 16.7 days; banking a 30-day dry spell needs 4,500 gal. Use USABLE storage (above the pump intake and below overflow, past any fire or first-flush reserve) and a realistic peak demand, not the annual average. For a rain-fed cistern the reserve must bridge the longest dry spell between refills; for a hauled or well-fed tank it sets the refill interval. A planning estimate; local rainfall or the source yield, the storage detail, and the AHJ (for potable use) govern.
• Detention Time - Detention time = volume / flow in min, hr, days; pass/fail vs target.
• Lab Dilution and Serial Dilution - C1V1 = C2V2 missing-side solve; serial dilution series with per-step concentrations.
• Pump Wire-to-Water Efficiency - Water HP, brake HP estimate, and wire-to-water % with good/ok/degraded category.
• SRT and F/M Ratio - Solids retention time and food-to-microorganism ratio with conventional-activated-sludge check.
• Coagulant Dose from Jar Test - Pure equivalent + product feed (lb/day, gal/day) for alum, ferric chloride, or PAC at the jar-test optimal dose.
• Sludge Volume Index (SVI) - SVI = SV30 * 1000 / MLSS in mL/g, with operator-typical operational bands (typical / pin floc / filamentous / bulking). Companion to the srt-fm-ratio tile.
• Disinfection CT (USEPA SWTR) - CT achieved (C * t10) compared to USEPA SWTR Guidance Manual required CT for 3-log Giardia inactivation by temperature and pH. Bundled <= 0.4 mg/L free-chlorine table; state primacy agency table governs final compliance.
• Pool Turnover Rate and Chlorine Demand - Required pump flow from pool volume and turnover target, plus the chlorine product to dose a free-chlorine target (cal-hypo / trichlor / liquid bleach). Per the NSPF CPO Handbook and ANSI/APSP/ICC 11.
• Well Drawdown and Specific Capacity - Drawdown, specific capacity (GPM per ft), and recommended pump-setting depth, with a marginal-well flag below 0.5 GPM/ft. Per AWWA A100 and USGS OFR 02-197.
• Cooling Water Makeup (Cycles of Concentration) - Evaporation, blowdown, drift, and total makeup flow from recirculation, range, and cycles of concentration, with scaling and drift flags. Per CTI and ASHRAE Systems and Equipment 2020 Ch. 40.
• Chlorine Residual Decay (First-Order) - First-order residual C(t) = C0 x exp(-k t), time to a target residual, and an optional booster distance. Per EPA 815-R-02-020 and AWWA M14; 40 CFR 141.74 governs the extremity residual.
• Backflow Assembly Test Pass Criteria - Pass/fail per assembly type with the governing field-test criterion: RP relief opens >= 2 psid below the #1 check and the #1 check >= 5 psid; DC each check >= 1 psid. Per the USC FCCCHR Manual and AWWA C511.
• Weir / Flume Open-Channel Flow - Open-channel flow over a 90-degree V-notch or rectangular (Francis) weir in cfs, GPM, and MGD from the head over the crest and an editable weir coefficient.
• Weir Head from a Target Flow - The inverse of the weir-flow tile: the head over a sharp-crested weir needed to pass a target flow. V-notch H = (Q/C)^(1/2.48); suppressed rectangular H = (Q/(C L))^(2/3); the contracted weir's L - 0.2 H is solved by fixed-point iteration. A 90-degree V-notch passing 0.446 cfs needs 0.50 ft of head. Sizes a weir box or sets a staff-gauge mark for a design flow. Head below ~0.2 ft is a low-accuracy reading; free, non-submerged, ventilated flow required. The operator of record governs.
• Langelier Saturation Index - LSI and a corrosive/balanced/scaling interpretation from pH, temperature, calcium hardness, total alkalinity, and TDS.
• Chemical Metering-Pump Setting - Neat chemical (lb/day), solution feed (GPD and mL/min), and pump setting (% of max) from plant flow, target dose, solution strength, and specific gravity via the pounds formula.
• Clarifier Surface, Weir, and Solids Loading - Surface overflow rate = flow/area (gpd/ft^2), weir overflow = flow/weir (gpd/ft), solids loading = flow x MLSS x 8.34 / area. 1 MGD, 40 ft dia (1257 ft^2), MLSS 2500 -> SOR 796, weir 7,958, solids 16.6; double the flow and SOR passes the ~1000 limit (floc carryover). The state design criteria govern.
• BOD/TSS Mass Loading and Percent Removal - Load (lb/day) = MGD x mg/L x 8.34, removal% = (in - out)/in x 100. 1 MGD, 200 -> 20 mg/L -> 1,668 lb/day in, 1,501 removed, 90%; a 4 MGD plant carries 6,672 lb/day at the same 90% (load scales, efficiency does not). An effluent above influent flags an upset. The operator of record governs.
• Total Dissolved Solids from Conductivity - TDS (mg/L) = k x EC (uS/cm at 25 C), k commonly 0.55-0.75 (default 0.65). 1000 uS/cm -> 650 mg/L, with a 550-750 band from the k range so it is not read as exact. An estimate, not a gravimetric TDS; calibrate k to a lab result. The operator of record governs.
• Conductivity from Total Dissolved Solids - The inverse of the TDS estimate: EC (uS/cm at 25 C) = TDS (mg/L) / k, k commonly 0.55-0.75 (default 0.65). 650 mg/L -> 1000 uS/cm, with an 867-1182 band from the k range so it is not read as exact. Predicts a conductivity-meter reading from a target/permit TDS or sets an EC alarm setpoint. An estimate, not a measurement; calibrate k to a lab result. The operator of record governs.
• Population Equivalent (Organic Load) - The population equivalent of a discharge, figured three ways -- from BOD (0.17 lb/capita/day), flow (100 gpd/capita), and suspended solids (0.20 lb/capita/day) -- with the GOVERNING value being the largest, not BOD alone. A 0.5 MGD cannery at 600 mg/L BOD is worth ~14,700 residents in oxygen demand though its gallons look like 5,000; billing on flow alone under-charges it.
• Return Activated Sludge (RAS) Flow Rate - The return-pump rate from the solids mass balance: Q_RAS = Q x MLSS / (RAS_SS - MLSS), plus the return ratio. The clarifier only thickens sludge 3-4x, so RAS_SS is capped -- cranking the pump to chase a higher MLSS floods the clarifier and washes solids over the weir. The mass balance, not the pump maximum, sets the rate.
• Settleability-Based RAS Rate (from SVI) - The RAS number straight from the settleometer, no RAS_SS lab result needed: the achievable return concentration is Xr = 1,000,000 / SVI, so the ratio for a target MLSS is R = MLSS / (Xr - MLSS) and Q_RAS = R x Q. Poor settling forces a much higher return - holding 2,500 mg/L on a good SVI of 100 needs a 33% return, but a bulking sludge at SVI 150 wanting 3,000 mg/L needs 82%, and if the pumps cannot deliver it the MLSS target is unreachable. The settleometer path to the same mass balance ras-flow-rate does from a measured RAS_SS. An operating aid, not a process design.
• WAS Rate to Hold Target SRT (Sludge Age) - The daily wasting decision: how much sludge to waste today to hold a target SRT. Q_WAS = (system_solids/SRT - effluent_solids) / (WAS x 8.34), in MGD and gpm. The inverse of a sludge-age readout; effluent solids over the weir count as wasted and cut the pump rate. SRT lags ~one SRT, so change gradually.
• Anaerobic Digester Volatile Solids Loading - The digester health metric: volatile-solids loading rate VSLR = VS_fed / volume x 1000 (lb VS/day per 1,000 ft^3), the VS fed, and the detention time. Overloading past ~400 sours the digester (acid-formers outrun the methane-formers, pH crashes). The loading rate, not a full tank, is the metric; a rich feed can overload at low flow.
• Digester Volatile-Acid to Alkalinity Ratio - The early-warning stability index the pH meter misses: ratio = volatile acids / alkalinity (common CaCO3 basis). Below ~0.1 stable, 0.1-0.25 acceptable, 0.25-0.4 begin corrective action (cut feed, add alkalinity), above ~0.4 souring. The bicarbonate buffer holds the pH steady until the alkalinity is consumed, so the ratio flags the upset days before the pH moves. A digester at VA 900 / alkalinity 3,000 (ratio 0.30) needs action now while its pH still reads normal. An operating aid, not a control setpoint.
• Digester Gas and Methane Production - The payoff side of anaerobic digestion, from the volatile solids destroyed: gas = VS_destroyed x yield (12-18 ft^3/lb, default 15), methane = gas x ~65%, energy = methane x 960 BTU/ft^3. A digester destroying 5,500 lb VS/day makes about 82,500 ft^3 of gas, 54,000 ft^3 of methane, and 51 MMBtu/day - enough to heat the digester and run a cogeneration engine. Turns digester-vs-loading's healthy feed rate into the gas-and-energy number the plant budgets around. A planning estimate, not a metered gas measurement.
• Activated-Sludge Oxygen and Blower Air Demand - The oxygen the aeration system must supply and the blower air to deliver it: O2 = factor x BOD_removed + 4.6 x NH3_nitrified, air_scfm = O2 / (0.075 x 0.232 x SOTE x 1440). Nitrification adds 4.6 lb O2 per lb ammonia-N (easy to forget); diffused-aeration SOTE is only ~10-35%, so the air demand dwarfs the oxygen pounds. The largest energy cost at a plant.
• Mixing Velocity Gradient (G / Gt) - The Camp-Stein velocity gradient G = sqrt(P / (mu x V)) and the Gt product that set floc formation: rapid mix wants G 500-1,000/s, flocculation G 20-70/s. G depends on water temperature through viscosity -- cold water is more viscous, so the same paddle delivers a lower G in winter and can drop below the 20/s floor. Too high a G shears the floc apart.
• Tapered Flocculation G Schedule - The mixing power each stage of a tapered floc train needs: P_stage = G_stage^2 x mu(T) x V, the same Camp-Stein relation flocculation-g-value validated, inverted across 2-3 stages of decreasing G. A 50/30/20 per-second taper in three 100 m^3 stages at 15 C needs 285 / 102 / 46 W - the last stage runs at a sixth of the first, the gentle finish that grows settleable floc without shearing it. Reports the composite Gt and flags a schedule that is not tapered or steps outside the 10-100/s band. A design aid, not a process design.
• Paddle Flocculator Power from Geometry - The power flocculation-g-value needs, computed from the paddle wheel: P = 0.5 x Cd x rho x A x v_rel^3, the Newtonian drag. Two subtleties - the power goes as the CUBE of the relative velocity, and the water slips (rotates with the paddles) so v_rel is only (1 - k) of the tip speed; ignoring the slip roughly doubles the power. A 6-ft wheel at 3 rpm with 40 ft^2 of blade delivers ~267 W. Cd (~1.8) and slip k (~0.25) are user inputs because references disagree; the drag is exact once chosen. A design aid, not a metered power.
• Gas Chlorine Cylinder Withdrawal Rate - Whether a gas chlorine container can physically deliver the feed rate: a 150-lb cylinder tops out near 40 lb/day and a 1-ton container near 400 lb/day at ~70 F, derated in a colder room. Pull gas faster and the container frosts over and the rate collapses -- a latent-heat ceiling no bigger regulator beats. Returns the containers to manifold and a frost warning.
• Pool Waterline Tile and Coping Perimeter Takeoff - Waterline tile and coping around a pool perimeter: perimeter = 2 x (length + width); tiles = ceil(perimeter / tile length x courses x (1 + waste)); coping = ceil(perimeter / coping length x (1 + waste)). A 16 x 32 ft pool has a 96 ft perimeter, so one course of 6 in tile is 212 tiles (192 neat) and 12 in coping is 106 units (96 neat) at 10% waste; a second tile course doubles the tile to 423 while the coping holds. The perimeter is the rectangular case; a freeform pool is measured on the tape. Distinct from the water-volume pool-volume.
• Pool Gunite Shell and Plaster Volume - Gunite shell and plaster for a pool, both driven by the interior surface area: interior = length x width + 2 x (length + width) x avg depth; gunite = interior x shell / 27 x (1 + waste); plaster = interior x plaster / 27. A 15 x 30 ft pool averaging 5.5 ft deep has 945 sf of interior, so an 8 in gunite shell is 26.8 cy and a 3/8 in plaster coat is 1.1 cy; a deeper 7 ft average grows the interior to 1,080 sf and the gunite to 30.6 cy. Gunite rebound is on top (see shotcrete-rebound-quantity). Distinct from the water pool-volume.
• Gravity Oil/Water Separator Surface Area (API 421) - The minimum horizontal (plan) area of a gravity oil/water separator per API 421: an oil droplet rises at the Stokes velocity Vt = g(rho_w - rho_o)d^2/(18 mu), and the separator must let the design droplet reach the surface before the flow carries it out, so area = 1.2 x Q / Vt. A 150 micron droplet of 0.85-SG oil in 60 F water rises about 0.33 ft/min, so 50 gpm needs about 24 ft^2; 100 gpm needs 49. Colder water and smaller droplets slow the rise and demand more area, and an emulsified or dissolved oil fraction will NOT gravity-separate (it needs coalescing, DAF, or downstream treatment). A SCREEN, not a design; API 421, the manufacturer, and the engineer / AHJ govern the separator and the discharge permit.
• Pool Water Volume by Shape - The gallonage every pool dose and heater tile takes as its input: gallons = surface area x average depth x 7.48052, average depth = (shallow + deep)/2. Rectangle area L x W, round pi(D/2)^2, oval (pi/4)L x W. A 32 x 16 ft rectangle 3 to 8 ft deep is 512 ft^2 x 5.5 ft = 2,816 ft^3 = 21,065 gal. A field estimate; a metered fill or plan takeoff is more exact.
• Pool Total Alkalinity Adjustment - Sodium bicarbonate to raise or muriatic acid to lower total alkalinity, by pool volume and the ppm change -- the buffer a tech sets before pH. A starting dose to add in portions and retest.
• Pool Cyanuric Acid Dose - Cyanuric acid to raise stabilizer, or -- since CYA leaves only by dilution -- the fraction and gallons of water to replace to lower it. A starting dose to add slowly and retest.
• Pool Salt Dose - Pool salt to add for a salt-chlorine generator, or the water to replace to lower an over-salted pool, by a straight mass balance. Reported in pounds and 40-lb bags.
• Pool Calcium Hardness Increase (Calcium Chloride) - Calcium chloride to raise a pool's calcium hardness -- the level that, with pH and alkalinity, sets the LSI balance (soft water corrodes plaster and metal, hard water scales). Hardness is expressed as CaCO3, so the dose converts the CaCO3-equivalent (ppm x gal x 8.34e-6 lb) to calcium chloride by the molecular-weight ratio 110.98/100.09 and divides by the product's calcium-chloride content: raising 20,000 gal by 20 ppm with 77% flake takes ~4.8 lb, or ~1.2 lb per 10,000 gal per 10 ppm (the shop rule of thumb); anhydrous (~94%) needs less. CAUTION: calcium chloride releases heat dissolving -- add it slowly to a bucket of water (never the reverse), pour in with the pump running, retest. Hardness only dilutes DOWN (drain and refill). A starting dose; the test kit, the target (typically 200-400 ppm), the product label, and CPO practice govern.
• Pool Free-Chlorine Dose by Product - Free-chlorine dose = ppm x (gal/1e6) x 8.34 lb, divided by the product available-chlorine fraction, as dry oz or (liquid) fl oz. A 15,000 gal pool +2 ppm needs 6.2 oz of 65% cal-hypo, or 25.6 fl oz of 12.5% liquid. The product label governs.
• Pool Heater Sizing and Heat-Up Time - Heat-up energy Btu = gallons x 8.34 x rise, and time = energy/(output x efficiency). A 20,000 gal pool +10 F takes 5.2 h on a 400,000 Btu/h gas heater at 80%, but 11.1 h on a 150,000 Btu/h heat pump. Ignores cover/standby losses. The equipment ratings govern.
• Pool Heater Output for a Target Heat-Up Time - The inverse of the pool-heater-btu tile: the heater output needed to warm a pool by a rise in a target time, output = (gallons x 8.34 x rise) / (target_hours x efficiency). Warming a 20,000 gal pool +10 F in 5.2 h at 80% needs a 400,000 Btu/h heater; ask for it in 3 h and it jumps to 695,000 Btu/h. Answers 'what size heater do I need' instead of the time from one heater. Ignores cover/standby losses, so add margin. The equipment ratings govern.
• Breakpoint Chlorination Dose - Combined chlorine (chloramines) = total - free, and the breakpoint shock dose = ratio x combined (commonly 10:1). Total 1.5, free 1.0 -> 0.5 ppm combined, a 5 ppm shock; shock past breakpoint (a partial dose worsens it). The label and testing govern.
• Chlorine Demand and Dose for a Target Residual - The chlorine consumed by the water (applied minus the measured residual) and the dose to hold a target residual (demand + target). A high or rising demand points to ammonia or organics - check the breakpoint curve. Standard Methods 4500-Cl / AWWA M14; the state primacy agency sets the compliance residual and method.
• Dechlorination Chemical Dose - The sulfur-based chemical to neutralize a chlorine residual before an NPDES discharge or a fish-bearing stream: reagent dose (mg/L) = a stoichiometric ratio x the chlorine residual to remove; feed (lb/day) = dose x flow (MGD) x 8.34 / purity. The ratio (mg reagent per mg Cl2) is reagent-specific and editable: ~0.9-1.0 for SO2, 1.34 sodium metabisulfite, 1.46 sodium bisulfite, 1.77 sodium sulfite, ~0.56 sodium thiosulfate. Removing a 2.0 mg/L residual from 5 MGD with sodium bisulfite is a 2.92 mg/L dose and 121.8 lb/day of 100% product; less-pure product needs more. Sulfur dechlor consumes dissolved oxygen and depresses pH, so an over-dose has its own permit cost -- dose to just neutralize, and confirm a near-zero residual downstream of mixing. A dosing estimate; the discharge permit, the reagent assay, and the state primacy agency govern.
• Float-Method (Velocity-Area) Open-Channel Flow - A field estimate of open-channel flow (ditch, canal, outfall) with a float, a tape, and a stopwatch: Q = C x surface velocity x cross-sectional area. Time a float over a measured reach for the SURFACE velocity (distance/time), multiply by area (width x mean depth), and apply a float coefficient C to convert surface to the lower MEAN velocity -- C ~0.85 (0.8 rough/shallow to ~0.9 smooth/deep). A float running 20 ft in 10 s (2.0 ft/s) in a 4 ft x 1.5 ft channel gives 0.85 x 2.0 x 6 = 10.2 cfs (~4,580 gpm). Average several runs in the fastest thread, survey the real cross-section, use a straight uniform reach. A rough field gauging estimate, well below a metered measurement; a permit-compliance flow needs a calibrated device, and the metering standard and permit govern.
• Fluoride Feed Dose (Available Fluoride Ion) - The pounds-per-day of a fluoridation chemical to hit a target fluoride level -- the pounds formula (net dose x flow MGD x 8.34) with the two corrections the generic chemical-feed tile omits: divide by the AVAILABLE FLUORIDE ION (AFI) fraction and the commercial strength, and first SUBTRACT the raw background fluoride the water already carries. AFI is fixed per chemical: fluorosilicic acid (H2SiF6) 0.792, sodium fluoride (NaF) 0.452, sodium fluorosilicate (Na2SiF6) 0.607. Feeding a net 0.6 mg/L (0.7 target minus 0.1 raw) into 2 MGD with 25% fluorosilicic acid = 0.6 x 2 x 8.34 / (0.792 x 0.25) = 50.55 lb/day of acid, carrying 10.0 lb/day of fluoride ion. US PHS target 0.7 mg/L. A feed-setpoint aid; the daily lab checks, the SDWA maximum, the exact product assay, and the state fluoridation program govern.
• Chlorine Decay Constant from a Bottle Test - The inverse of the chlorine-decay tile: the first-order decay constant k from an initial and a measured residual over an elapsed time, k = ln(C0 / C) / t, with the half-life. A residual falling 2.0 -> 0.7358 mg/L in 10 h gives k = 0.100 1/hr (a 6.9 h half-life). The field number that feeds the forward decay and booster-spacing model. Per EPA 815-R-02-020 and AWWA M14.
• UV Dose and Target Check - The delivered ultraviolet dose (intensity x exposure time, mW.s/cm^2 = mJ/cm^2) checked against a validated target (default 40 mJ/cm^2). A short dose points to an aged lamp, a fouled sleeve, or low UV transmittance. USEPA UV Disinfection Guidance; the validated reactor dose and the state primacy agency govern compliance.
• UV Required Intensity or Contact Time - The inverse of the UV-dose tile: from a target dose, solve the operand you are missing - leave intensity blank for the required contact time (dose / intensity), or leave time blank for the required intensity (dose / time). A 40 mJ/cm^2 target at 10 mW/cm^2 needs 4 s of contact; at a fixed 8 s it needs a 5 mW/cm^2 lamp. USEPA UV Disinfection Guidance; the validated reactor dose and the state primacy agency govern compliance.
• Well Sustainable Yield from Specific Capacity - The inverse of the well-drawdown tile: the sustainable pumping rate a well gives up without pulling the water below the pump, max_yield = specific_capacity x allowable_drawdown. A 1.0 GPM/ft well with 30 ft of usable drawdown (static to a safe level above the pump) yields 30 GPM; a marginal 0.3 GPM/ft well with 40 ft yields only 12 GPM. Answers 'how hard can I pump it' instead of the specific capacity from one test. Specific capacity declines with rate, so confirm with a constant-rate test. AWWA A100 / USGS; the well driller governs.
• Detention Basin Volume for a Target Time - The inverse of the detention-time tile: the basin volume required to hold flow for a target detention time, volume = target_minutes x flow. 120 min of contact at 350 GPM needs 42,000 gal. Sizes chlorine-contact, flocculation, and sedimentation basins. Ten States Standards; the reviewing authority governs.
• Filter Area for a Target Loading Rate - The inverse of the filter-loading tile: the filter area needed for a target loading rate at the design flow, area = flow / target loading. 800 GPM at 4 gpm/ft^2 needs 200 ft^2 of media; the backwash flow that area draws (15 gpm/ft^2 default) is reported and the loading band named. Answers 'how big a filter' instead of the rate from one area. AWWA general practice; the operator of record and the state primacy agency govern.
• Clarifier Surface Area for a Target SOR - The inverse of the clarifier-loading tile: the clarifier surface area a target surface overflow rate needs at the design flow, area = flow x 1e6 / SOR, plus the equivalent circular clarifier diameter. 1 MGD at 800 gpd/ft^2 needs 1,250 ft^2 (about a 40 ft diameter). Answers 'how big a clarifier' instead of the rate from one area; size below the limit for peak flow. A separate weir and solids check governs alongside. Ten States Standards; the state primacy agency governs.