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A detailed summary of RO influent quality is presented in Table 6 for the period of January through October 2012, compared to the specified design influent quality. Both 50th and 90th percentile values are presented. Influent values exceeding the specified design values are indicated in bold. The principal issues indicated by these data are iron and manganese (because of potential oxidation and fouling of the RO membranes), and nitrogen and phosphate species (because of the stringent reclaimed water discharge standards and potential for precipitation of calcium phosphate within the second stage of the RO system). Actual total dissolved solids (TDS) values were significantly less than the design value. Even considering that operating temperatures were generally lower than the 90th percentile design value of 26 °C, the head on the RO feed pumps was more than sufficient to achieve the specified flux and recovery at the observed TDS values.

Table 6

Comparison of RO feedwater quality for 12 January through 22 October 2012 compared to specified design values

	Design		Actual
Parameter, mg/L	50th %tile	90th %tile	50th %tile	90th %tile
Ca	20.1	29.7	24.1^a	28.1
Mg	6.6	9.5	7.4	8.9
Na	161	190	121.6	138
K	21.6	31.2	15	16.9
Ba	0.07	0.12	< 0.01	< 0.01
Sr	0.08	0.08	< 0.01	0.1
Al	0.04	0.04	NM^b	NM
Fe	0.07	0.11	0.2	0.37
Mn	0.06	0.06	0.26	0.35
Alkalinity as CaCO₃	146	192	127	151
Bicarbonate as CaCO₃	178	234	155	184
Cl	158	190	100	117
SO₄⁻²	72.2	94.4	55.0	65.9
Fl	0.95	0.95	0.22	0.28
Br	0.00	0.00	0.26	0.42
NH₃-N^c	0.18	0.18	1.24	2.46
NO₂-N	0.39	0.45	0.00	0.09
NO₃-N	0.70	1.43	0.78	2.19
Organic nitrogen	2.06	1.27	1.89	1.94
TN	3.33	3.33	3.91	6.68
PO₄-P	1.00	1.00	2.00	4.45
TP	1.00	1.00	2.70	4.75
Si	17.1	17.27	NM	NM
B	0.22	0.23	NM	NM
Conductivity, uS/cm	1006	1247	758	859
TDS	644	804	485	554
Total hardness, as CaCO₃	66	111	91	107
pH, units	7.01	7.00	7.18	7.53
Temperature, deg C	19	26	17.1	21.2
Turbidity, NTU	NE^d	NE	0.030	0.080
SDI, 15-min	NE	NE	2.4	3.28
TOC	NE	NE	13.3	19.5
Total carbon	NE	NE	52.6	63.8
Colour, Pt Co	NE	NE	51.5	77.1
UV254, 1/cm	NE	NE	0.35	0.50
Chloramines, as NH₂Cl	3.0	3.0	1.52	2.14
Chloramines, as NH₃	0.82	0.82	0.50	0.71

	Design		Actual
Parameter, mg/L	50th %tile	90th %tile	50th %tile	90th %tile
Ca	20.1	29.7	24.1^a	28.1
Mg	6.6	9.5	7.4	8.9
Na	161	190	121.6	138
K	21.6	31.2	15	16.9
Ba	0.07	0.12	< 0.01	< 0.01
Sr	0.08	0.08	< 0.01	0.1
Al	0.04	0.04	NM^b	NM
Fe	0.07	0.11	0.2	0.37
Mn	0.06	0.06	0.26	0.35
Alkalinity as CaCO₃	146	192	127	151
Bicarbonate as CaCO₃	178	234	155	184
Cl	158	190	100	117
SO₄⁻²	72.2	94.4	55.0	65.9
Fl	0.95	0.95	0.22	0.28
Br	0.00	0.00	0.26	0.42
NH₃-N^c	0.18	0.18	1.24	2.46
NO₂-N	0.39	0.45	0.00	0.09
NO₃-N	0.70	1.43	0.78	2.19
Organic nitrogen	2.06	1.27	1.89	1.94
TN	3.33	3.33	3.91	6.68
PO₄-P	1.00	1.00	2.00	4.45
TP	1.00	1.00	2.70	4.75
Si	17.1	17.27	NM	NM
B	0.22	0.23	NM	NM
Conductivity, uS/cm	1006	1247	758	859
TDS	644	804	485	554
Total hardness, as CaCO₃	66	111	91	107
pH, units	7.01	7.00	7.18	7.53
Temperature, deg C	19	26	17.1	21.2
Turbidity, NTU	NE^d	NE	0.030	0.080
SDI, 15-min	NE	NE	2.4	3.28
TOC	NE	NE	13.3	19.5
Total carbon	NE	NE	52.6	63.8
Colour, Pt Co	NE	NE	51.5	77.1
UV254, 1/cm	NE	NE	0.35	0.50
Chloramines, as NH₂Cl	3.0	3.0	1.52	2.14
Chloramines, as NH₃	0.82	0.82	0.50	0.71

^aBold values represent measured values that exceed corresponding design values.

^bNM, not measured.

^c50th and 90th percentile NH₃-N levels in MBR filtrate prior to ammonia dosing were 0.20 and 3.6 mg/L, respectively.

^dNE, none established.

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